זמנים
הלכות חמץ ומצה
פרק ב

Halacha

הלכה א
מִצְוַת עֲשֵׂה מִן הַתּוֹרָה לְהַשְׁבִּית הֶחָמֵץ קֹדֶם זְמַן אִסּוּר אֲכִילָתוֹ שֶׁנֶּאֱמַר (שמות יב טו) "בַּיּוֹם הָרִאשׁוֹן תַּשְׁבִּיתוּ שְּׂאֹר מִבָּתֵּיכֶם". וּמִפִּי הַשְּׁמוּעָה לָמְדוּ שֶׁבָּרִאשׁוֹן זֶה הוּא יוֹם אַרְבָּעָה עָשָׂר. רְאָיָה לְדָבָר זֶה מַה שֶּׁכָּתוּב בַּתּוֹרָה (שמות לד כה) "לֹא תִשְׁחַט עַל חָמֵץ דַּם זִבְחִי" כְּלוֹמַר לֹא תִּשְׁחַט הַפֶּסַח וַעֲדַיִן הֶחָמֵץ קַיָּם. וּשְׁחִיטַת הַפֶּסַח הוּא יוֹם אַרְבָּעָה עָשָׂר אַחַר חֲצוֹת:
כסף משנה
1.
It is a positive commandment from the Torah to destroy chametz before the time it becomes forbidden to be eaten, as1The Rambam describes the more practical aspects of the nullification of chametz in Chapter 3, Halachot 7-10. There, he requires a person to make a formal statement nullifying his chametz. That declaration is a Rabbinic requirement. According to the Torah itself, a firm resolve is sufficient, and no statement is necessary (Binyan Shlomo). [Exodus 12:15] states: "On the first day, destroy leaven from your homes." On the basis of the oral tradition, it is derived that "the first day" refers to the day of the fourteenth.
Proof of this matter is the verse from the Torah [Exodus 34:25]: "Do not slaughter the blood of My sacrifice with chametz," i.e., Do not slaughter the Pesach sacrifice while chametz exists [in your possession]. The slaughter of the Pesach sacrifice was on the fourteenth after midday.

הלכה ב
וּמַה הִיא הַשְׁבָּתָה זוֹ הָאֲמוּרָה בַּתּוֹרָה הִיא שֶׁיְּבַטֵּל הֶחָמֵץ בְּלִבּוֹ וְיַחֲשֹׁב אוֹתוֹ כְּעָפָר וְיָשִׂים בְּלִבּוֹ שֶׁאֵין בִּרְשׁוּתוֹ חָמֵץ כְּלָל. וְשֶׁכָּל חָמֵץ שֶׁבִּרְשׁוּתוֹ הֲרֵי הוּא כְּעָפָר וּכְדָבָר שֶׁאֵין בּוֹ צֹרֶךְ כְּלָל:
כסף משנה
2.
What is the destruction to which the Torah refers? to nullify chametz within his heart1The Kessef Mishneh quotes a different version of the text:What is the destruction to which the Torah refers? to remove all chametz known to one from his property. [The chametz] which is unknown should be nullified...This version implies that, according to Torah as well as Rabbinic law (See Halachah 2), we must rid our homes of all chametz of whose existence we are conscious; its nullification is not sufficient.
Nevertheless, the Kessef Mishneh brings a number of proofs from the Talmud and also quotes other commentaries of the Rambam, which maintain that the published text is correct and that the nullification of chametz is sufficient according to Torah law. He also quotes Hilchot Berachot 11:15, which emphasizes that "from the moment a person resolves in his heart to nullify it, the mitzvah of destroying [chametz] is fulfilled."
and to consider it as dust,2The Rambam describes the more practical aspects of the nullification of chametz in Chapter 3, Halachot 7-10. There, he requires a person to make a formal statement nullifying his chametz. That declaration is a Rabbinic requirement. According to the Torah itself, a firm resolve is sufficient, and no statement is necessary (Binyan Shlomo). and to resolve within his heart that he possesses no chametz at all:2doing so removes his legal ownership over the chametz. all the chametz in his possession being as dust and as a thing of no value whatsoever.2If a person nullifies chametz within his heart and genuinely does not consider it as belonging to him, Torah law does not obligate him for the possession of chametz even if large quantities of it are found within his home.

הלכה ג
וּמִדִּבְרֵי סוֹפְרִים לְחַפֵּשׂ אַחַר הֶחָמֵץ בַּמַּחֲבוֹאוֹת וּבַחוֹרִים וְלִבְדֹּק וּלְהוֹצִיאוֹ מִכָּל גְּבוּלוֹ. וְכֵן מִדִּבְרֵי סוֹפְרִים שֶׁבּוֹדְקִין וּמַשְׁבִּיתִין הֶחָמֵץ בַּלַּיְלָה מִתְּחִלַּת לֵיל אַרְבָּעָה עָשָׂר לְאוֹר הַנֵּר. מִפְּנֵי שֶׁבַּלַּיְלָה כָּל הָעָם מְצוּיִין בַּבָּתִּים וְאוֹר הַנֵּר יָפֶה לִבְדִיקָה. וְאֵין קוֹבְעִין מִדְרָשׁ בְּסוֹף יוֹם שְׁלֹשָׁה עָשָׂר. וְכֵן הֶחָכָם לֹא יַתְחִיל לִקְרוֹת בְּעֵת זוֹ שֶׁמָּא יִמָּשֵׁךְ וְיִמָּנַע מִבְּדִיקַת חָמֵץ בִּתְחִלַּת זְמַנָּה:
כסף משנה
3.
According to the Sages' decree,1As explained in the previous halachah, according to the Torah, chametz may be within a person's property as long as he declared it ownerless. Nevertheless, the Sages forbade such practices and required all chametz to be removed from one's property.
Two reasons are given for this decree:
a) The nullification of chametz is dependent on the feelings of a person's heart. A person may possibly have difficulty totally removing all thoughts of ownership over the chametz from his heart (Rabbenu Nissim, Pesachim 2a).
b) In contrast to other prohibited substances, chametz is used throughout the year. Thus, were he allowed to leave chametz within his property, he might accidentally forget about the prohibition and eat it on Pesach (Tosefot, Pesachim 2a).
In addition to the restriction against possessing chametz, the Sages further expanded the scope of
[the mitzvah2to destroy chametz so that it involves] searching for chametz3It must be emphasized that the obligation to search for chametz is Rabbinic in nature only when a person nullifies his chametz when required. Otherwise, the obligation stems from the Torah, for the prohibitions against possessing chametz and the commandment to destroy it require such a search. The Tzafnat Paneach quotes a number of examples that demonstrate how the existence of a Torah commandment obligates a person to check and search to see that it is being fulfilled correctly. in hidden places and in any holes [within one's house],4as clarified in Halachah 6, the obligation to search applies only to those holes and crevices in which chametz is usually placed. seeking it5Bedikat chametz and removing it from all of one's domain.6Biyur chametz.
Similarly, according to the Sages' decree, we must search [with the intent to] destroy chametz by candlelight, at night,7The destruction of chametz at night refers to the statement חמירא כל, in which we nullify all the chametz of whose possession we are unaware. The chametz that we know about is either eaten or destroyed the next morning. at the beginning of the night of the fourteenth [of Nisan].8i.e., the night between the thirteenth and fourteenth of Nisan. [They instituted the search at that time]9in contrast to the day of the fourteenth, when the prohibition against possessing chametz begins (Pesachim 4a). because all people are at home at night,10while during the day people are occupied outside their homes. and the light of the candle is good for searching.11during the day, its light would not be as effective.
A study session should not be fixed for the end of the thirteenth of Nisan.12Rabbenu Yonah allows a person to continue a study session on the night of the fourteenth if the session began while it was still day. Rav Yosef Karo accepts his opinion, but the Ramah does not. However, the Taz explains that leniencies may be made for public study sessions. Shulchan Aruch HaRav and the Mishnah Berurah go further and allow public study sessions even after nightfall, provided the subject matter is not overly involving. Similarly, a wise man should not begin to study at this time,13half an hour before nightfall (Magen Avraham, Orach Chayim 431:3). lest he become involved,14The Maggid Mishneh mentions that it is also improper to begin a meal at this time. The Shulchan Aruch (Orach Chayim 431:2) also prohibits beginning work. Communal prayer is allowed. and thus be prevented from searching for chametz at the beginning of the time.15There are two reasons for the preference in carrying out the search in the beginning of the night:
a) it is appropriate to carry out a mitzvah as soon as possible;
b) at the beginning of the night, there is still some daylight left, which will facilitate the search (Ra'avad, Commentary on the Rif).

הלכה ד
אֵין בּוֹדְקִין לֹא לְאוֹר הַלְּבָנָה וְלֹא לְאוֹר הַחַמָּה וְלֹא לְאוֹר הָאֲבוּקָה אֶלָּא לְאוֹר הַנֵּר. בַּמֶּה דְּבָרִים אֲמוּרִים בְּחוֹרִים וּבְמַחֲבוֹאוֹת אֲבָל אַכְסַדְרָה שֶׁאוֹרָהּ רַב אִם בְּדָקָהּ לְאוֹר הַחַמָּה דַּיּוֹ. וְאֶמְצַע הֶחָצֵר אֵינוֹ צָרִיךְ בְּדִיקָה מִפְּנֵי שֶׁהָעוֹפוֹת מְצוּיִים שָׁם וְהֵן אוֹכְלִין כָּל חָמֵץ שֶׁיִּפּל שָׁם:
כסף משנה
4.
We do not search [for chametz] by the light of the moon, the light of the sun,1if one searches by day; i.e., either one forgot to search on the night of the thirteenth and had to carry out the search the following day. Alternatively, one decided to search for chametz before the fourteenth of Nisan with the intention of keeping the room chametz-free afterwards (Jerusalem Talmud, Pesachim 1:1). The light of the sun is insufficient to check indoor areas carefully. or the light of a torch;2Pesachim 8a explains that a person will be scared to placed a torch close enough to check small holes and crevices carefully lest he start a fire. only by the light of a candle.3It is customary to use a candle made from beeswax. To what does this apply? to the holes and hidden places. However, for a porch4a room with three walls and the fourth side open. which has much light,5Pesachim 8a states that the same principle applies to the area directly under an aperture in the roof. The Magen Avraham (Orach Chayim 433:4) also applies this principle to the area directly opposite an open window. searching it by the light of the sun is sufficient.6The Rambam's choice of phraseology clearly implies that it is not desirable to do so. Rather, even a porch should be checked at night by candlelight. Other authorities question this perspective, but it is accepted as halachah by the Shulchan Aruch (Orach Chayim 433:1).
The middle of a courtyard7Pesachim 8a states "a courtyard need not be searched." The Rambam adds the words "the middle" out of fear that the birds will not eat the chametz in the cracks and holes close to the wall. In this case as well, though other authorities are more lenient, the Shulchan Aruch (ibid. 433:6) quotes the Rambam's opinion. does not need to be searched, because birds are found there, and they eat all the chametz which falls there.

הלכה ה
חוֹר שֶׁבְּאֶמְצַע הַבַּיִת שֶׁבֵּין אָדָם לַחֲבֵרוֹ זֶה בּוֹדֵק עַד מָקוֹם שֶׁיָּדוֹ מַגַּעַת וְזֶה בּוֹדֵק עַד מָקוֹם שֶׁיָּדוֹ מַגַּעַת וְהַשְּׁאָר מְבַטְּלוֹ בְּלִבּוֹ. אֲבָל חוֹר שֶׁבֵּין יִשְׂרָאֵל לְעַכּוּ''ם אֵינוֹ בּוֹדֵק כְּלָל שֶׁמָּא יֹאמַר הָעַכּוּ''ם כְּשָׁפִים הוּא עוֹשֶׂה לִי אֶלָּא מְבַטְּלוֹ בְּלִבּוֹ וְדַיּוֹ. וְכָל מָקוֹם שֶׁאֵין מַכְנִיסִין בּוֹ חָמֵץ אֵינוֹ צָרִיךְ בְּדִיקָה:
כסף משנה
5.
A hole1The Shulchan Aruch (Orach Chayim 433:4) applies the same principle to protrusions extending from a wall. in the middle2neither very high or low, see the following halachah. of [the wall of] the house3In previous generations, the walls of the homes were very thick and large holes would frequently be used for storage. between a person and his colleague [should be searched by both individuals],4for both may use it. each searching to the extent his hand reaches. [Afterwards,] each must nullify in his heart [any chametz in] the remaining portion.5As mentioned in Halachah 2, according to Torah law, the nullification of chametz is sufficient.
[This applies to a hole in a wall separating two Jewish homes.] However, a hole between [the home of] a Jew and a gentile should not be searched at all, lest the gentile6see the Jew looking intently through the hole by candlelight and fear that the Jew is casting spells against him.7This might motivate him to harm the Jew. The Sages did not require a Jew to endanger himself to fulfill their decrees. All that is necessary for him to do is to nullify it within his heart.8The Kessef Mishneh (and similarly, the Taz) require the Jew to check the hole for chametz by day.
Any place where chametz is not brought in does not need to be searched.9This is a major principle governing the search for chametz. The Sages only obligated a search where it was likely that chametz might be found. Therefore, they did not require a person to search places into which he did not bring chametz. Nevertheless, places where babies might have brought chametz must be searched, even though adults might not necessarily bring chametz there.

הלכה ו
חוֹרֵי הַבַּיִת הַתַּחְתּוֹנִים וְהָעֶלְיוֹנִים וְגַג הַיָּצִיעַ וְרֶפֶת בָּקָר וְלוּלִין וּמַתְבֵּן וְאוֹצְרוֹת יַיִן וְאוֹצְרוֹת שֶׁמֶן שֶׁאֵינוֹ מִסְתַּפֵּק מֵהֶן וּבֵית דָּגִים גְּדוֹלִים אֵינָן צְרִיכִין בְּדִיקָה אֶלָּא אִם כֵּן הִכְנִיס לָהֶן חָמֵץ. אֲבָל אוֹצְרוֹת שֵׁכָר וְאוֹצְרוֹת יַיִן שֶׁמִּסְתַּפֵּק מִמֶּנּוּ וּבֵית דָּגִים קְטַנִּים וּבֵית הָעֵצִים וּבֵית הַמּוּרְיָס וְחוֹרֵי הַבַּיִת הָאֶמְצָעִים וְכַיּוֹצֵא בָּאֵלּוּ צְרִיכִין בְּדִיקָה שֶׁסְּתָמָן שֶׁמַּכְנִיסִין לָהֶן חָמֵץ. וְאִם יָדַע בְּוַדַּאי שֶׁלֹּא הִכְנִיס שָׁם חָמֵץ אֵינוֹ צָרִיךְ בְּדִיקָה. וּכְשֶׁבּוֹדֵק הַמַּרְתֵּף בּוֹדֵק מִמֶּנּוּ שְׁתֵּי שׁוּרוֹת הַחִיצוֹנוֹת שֶׁהֵן הָעֶלְיוֹנָה וְשֶׁלְּמַטָּה מִמֶּנָּה:
כסף משנה
6.
The upper1those above a person's reach (Shulchan Aruch, Orach Chayim 433:4) and lower holes2below three handbreadths high (ibid.). The Magen Avraham (433:8) emphasizes that if children are found at home, these lower holes must also be searched. [in the wall] of a house,3This halachah continues the final clause of the previous one, listing a number of places into which chametz is generally not brought. the roof of a balcony,4The commentaries explain that this refers to slanted roofs. a cow stall, chicken coop,5Rashi, Pesachim 8a, explains that most likely, the animals and the chickens will eat any chametz brought there. Nevertheless, the Shulchan Aruch (ibid. 433:6) qualifies this leniency explaining that it does not apply when a person definitely knows that chametz was brought into these premises one month before Pesach. (See Magen Avraham; the Makor Chayim brings a more lenient opinion.) In such an instance, he must search the premises on the night of the thirteenth by candlelight. hayloft, wine cellars or storage rooms for oil when supplies are not taken from them [in the midst of a meal],6Hence, there is little possibility that chametz was brought there. and storage rooms for large fish,7Small fish may be taken out during the course of a meal. However, generally, a person will take large fish to prepare only before a meal and not in the midst of eating. need not be searched unless one brought chametz into them.8need not be searched unless one brought chametz into them.
In contrast, storage rooms for beer, storage rooms for wine from which supplies are taken [in the midst of a meal], storage rooms for salt, candles, small fish, wood, and brine,9In all these cases, the Sages regarded it likely that a person would get up in the middle of a meal while holding chametz in his hand to bring supplies from these storage rooms. Hence, they required such premises to be searched. the middle holes in a wall,10On the surface, these holes were mentioned in the previous halachah, and their mention here is redundant. and all similar places must be searched, for chametz is usually brought into them.11Thus, unless a person knows otherwise, he must act under the presumption that he brought chametz into these premises. However, if a person knows that he did not bring chametz into these places, they do not have to be searched.12However, if a person knows that he did not bring chametz into these places, they do not have to be searched.
When searching a wine cellar,13where barrels of wine are stacked one on top of the other so that a person cannot enter the area where they have been placed [all that is necessary to] search are the two outer rows—i.e., the highest row and the one below it.

הלכה ז
אֵין חוֹשְׁשִׁין שֶׁמָּא גָּרְרָה חֻלְדָּה חָמֵץ לְמָקוֹם שֶׁאֵין מַכְנִיסִין בּוֹ חָמֵץ שֶׁאִם נָחוּשׁ מִבַּיִת לְבַיִת נָחוּשׁ מֵעִיר לְעִיר וְאֵין לַדָּבָר סוֹף. בָּדַק לֵיל אַרְבָּעָה עָשָׂר וְהִנִּיחַ עֶשֶׂר חַלּוֹת וּמָצָא תֵּשַׁע הֲרֵי זֶה חוֹשֵׁשׁ וְצָרִיךְ לִבְדֹּק פַּעַם שְׁנִיָּה שֶׁהֲרֵי גָּרְרָה חֻלְדָּה אוֹ עַכְבָּר בְּוַדַּאי:
כסף משנה
7.
We do not suspect that a weasel dragged chametz into a place where it is not usually brought.1Pesachim 9a states: "We do not suspect that a weasel dragged chametz from one house to another or from place to place." Rashi explains that this statement applies after the search for chametz was carried out. Once we have searched our homes, we need not worry that rodents brought new chametz there.
In contrast, the Rambam interprets the statement as applying before the search. There is no need to suspect that perhaps a rodent took chametz from a place where chametz is usually kept to a place where it is not usually brought. The Kessef Mishneh emphasizes that the two interpretations are not contradictory and both are halachically applicable.
Were we to suspect [that chametz would be taken] from house to house, we would also have to suspect [that chametz might be taken] from city to city. There is no end to the matter.2There is always the possibility that chametz will be taken from one house to another. Hence, the Sages decided to ignore this possibility entirely.
A person who checked on the night of the fourteenth3as required and placed ten loaves of chametz [on the side]4to be used the following morning and [later] found [only] nine must suspect [that chametz is present in his home,] and [hence], must search a second time,5The Shulchan Aruch HaRav (Orach Chayim 439:7) relates that he may stop the second search as soon as one loaf is found. He may presume that this was the loaf that he originally put aside. for definitely it was taken by a weasel or mouse.6The rodent may have eaten the chametz or removed it from the premises entirely. Nevertheless, a new search is required, for it is also possible that some chametz was left within the house (Pesachim 9a).
As mentioned in Halachot 2 and 3, according to Torah law we need not do anything more than negate our ownership over our chametz. Nevertheless, the Sages also required that we search for chametz and destroy it completely. However, when a person does not nullify his chametz, the obligation to search takes on the severity of a Torah commandment.
This and the following halachot (8 through 13) deal with circumstances which raise questions whether a second search is required. Throughout these halachot, the Rambam makes no mention of whether the owner of the house previously nullified his chametz or not. This fact is extremely important, for different principles apply to an obligation required by Torah law from those that apply to one instituted by the Rabbis. Indeed, other Rabbinic authorities (some of whom are quoted in the commentaries to the various halachot) devote much attention to this issue, clarifying at length whether the laws apply:a) only when a person had already nullified (or can still nullify) his chametz, or;
b) even when the search for chametz is required by Torah law.Since the Rambam does not explicitly state his opinion on this matter, it is impossible to be sure which perspective he adopts. However, when the chapter is considered in its entirety, it appears that these halachot describe a situation where chametz has already been nullified. Unless specified to the contrary, this should be assumed to be the case. Nevertheless, certain of the leniencies are also applicable even when the search takes on the severity of a Torah obligation.

הלכה ח
וְכֵן אִם רָאָה עַכְבָּר שֶׁנִּכְנַס לַבַּיִת וְחָמֵץ בְּפִיו אַחַר בְּדִיקָה צָרִיךְ לִבְדֹּק פַּעַם שְׁנִיָּה אַף עַל פִּי שֶׁמָּצָא פֵּרוּרִין בְּאֶמְצַע הַבַּיִת אֵין אוֹמְרִין כְּבָר אָכַל אוֹתָהּ הַפַּת בְּמָקוֹם זֶה וַהֲרֵי הַפֵּרוּרִין אֶלָּא חוֹשְׁשִׁין שֶׁמָּא הִנִּיחָה בְּחוֹר אוֹ בְּחַלּוֹן וְאִלּוּ הַפֵּרוּרִין שָׁם הָיוּ. וּלְפִיכָךְ חוֹזֵר וּבוֹדֵק. אִם לֹא מָצָא כְּלוּם הֲרֵי זֶה בּוֹדֵק כָּל הַבַּיִת וְאִם מָצָא אוֹתָהּ הַפַּת שֶׁנְּטָלָהּ הָעַכְבָּר וְנִכְנַס אֵין צָרִיךְ בְּדִיקָה:
כסף משנה
8.
Similarly, a person who saw a mouse enter the house with chametz in its mouth after he searched [for chametz] must search a second time.1In this instance as well, there is an obvious reason for the suspicion that chametz has been brought into the home. [This applies] even if he found crumbs in the middle of the house; we do not necessarily presume that it already ate the bread in this place and that these are its crumbs.2for mice do not generally crumble food. (See the following halachah.) Rather, we suspect that it left the bread in a hole or window, and that these crumbs were [originally] located there.3and accidentally ignored, and the mouse deposited the bread it was carrying elsewhere. Hence, he must search again.4Though some authorities do not require a second search when the bread was small and most probably eaten by the mouse, the Shulchan Aruch HaRav and the Mishnah Berurah (Orach Chayim 438) do not accept this leniency.
If he does not find anything, he must search through the entire house.5The Shulchan Aruch (Orach Chayim 438:1) quotes this opinion as halachah. The Magen Avraham (based on the Tur) is more lenient. Rather than require that the entire house be searched, he maintains that searching the room that the mouse entered is sufficient. If he found the bread6even if it was no longer whole that the mouse took when he entered,7He must be able to recognize this as the bread seen in the mouse's mouth he need not search [further].8and may presume that the mouse ate the rest of the bread.

הלכה ט
רָאָה תִּינוֹק שֶׁנִּכְנַס לְבַיִת בָּדוּק וּבְיָדוֹ כִּכָּר וְנִכְנַס אַחֲרָיו וּמָצָא פֵּרוּרִין אֵינוֹ צָרִיךְ בְּדִיקָה שֶׁחֶזְקָתוֹ שֶׁאֲכָלוֹ וְאֵלּוּ הַפֵּרוּרִין שֶׁנָּפְלוּ מִמֶּנּוּ בִּשְׁעַת אֲכִילָה שֶׁדֶּרֶךְ הַתִּינוֹק לְפָרֵר בְּעֵת אֲכִילָתוֹ וְאֵין דֶּרֶךְ עַכְבָּר לְפָרֵר. וְאִם לֹא מָצָא פֵּרוּרִין כְּלָל צָרִיךְ לִבְדֹּק:
כסף משנה
9.
[A person who] saw an infant enter an already checked house1checked for chametz with bread in his hand, followed him inside and discovered crumbs, need not search [again].2The Magen Avraham (Orach Chayim 438:3) explains that if the child is intelligent enough to reply to questions, we should ask him what he did with the chametz and we may depend upon his reply. We may confidently assume that he ate the bread and that these crumbs fell from him while eating.3Tosefot (Pesachim 10b) require a second search if the amount of crumbs does not equal the quantity of the original bread. The Shulchan Aruch HaRav and the Mishnah Berurah favor the Rambam's opinion only when the person has nullified his ownership over his chametz. If not, the search takes on the seriousness of a Torah commandment. Hence, it must be repeated. Infants generally crumble food while eating, though mice do not.4Hence, the difference between this and the previous halachah.
If he does not find any crumbs, he must check [again].5and the principles mentioned in the previous halachah apply.

הלכה י
הִנִּיחַ תִּשְׁעָה צְבוּרִין שֶׁל מַצָּה וְאֶחָד שֶׁל חָמֵץ וּבָא עַכְבָּר וְנָטַל וְלֹא יָדַעְנוּ אִם חָמֵץ אוֹ מַצָּה נָטַל וְנִכְנַס לְבַיִת בָּדוּק צָרִיךְ לִבְדֹּק שֶׁכָּל הַקָּבוּעַ כְּמֶחֱצָה עַל מֶחֱצָה:
כסף משנה
10.
Nine piles of matzah and one of chametz were placed [aside].1For example, after the search for chametz, a person will still have some chametz in his property for use the following morning. However, he may already bring out his Passover matzot. A mouse came and took [something from one of the piles]2The Mishnah Berurah emphasizes that this decision applies only when we actually saw the mouse take from the piles. If no one saw the mouse, the ruling mentioned in the last clause of the following halachah applies. and entered a house that had been checked.3for chametz If we do not know whether it took either chametz or matzah, the house must be checked [again],4as if it were definitely chametz, as prescribed in Halachah 8. for every instance where [a doubt arises and the presence of both the permitted and forbidden substances] is fixed, [is judged] as if they5the permitted and forbidden substances were present in equal amounts.6The probability that the mouse took from the matzot is considered no greater than the probability that he took from the chametz.
This is a classic Talmudic case. Pesachim 9b draws a parallel to the following passage:Nine butcher shops which all sell ritually slaughtered meat and one which sells meat which has not been slaughtered properly: should a person take meat from one of them without knowing from which he took (i.e., without knowing whether he purchased kosher or non-kosher meat), he must consider [the meat] forbidden because of the doubt involved.In both cases, the permitted and forbidden substances remain in one place, and their existence is therefore considered as fixed (קבוע). In such instances, the fact that there is a much higher probability that the article in question was taken from the permitted substances is not considered significant, and the more stringent perspective is taken. See also Hilchot Ma'achalot Assurot 8:11.
Nevertheless, the Ra'avad and other authorities take issue with this halachah, explaining that the Talmud only made such a statement when a person has not nullified his chametz, and the responsibility to search the house stems from the Torah itself. However, if the person already nullified his chametz, the search is only a Rabbinic obligation. Hence, it should be judged more leniently.
The Maggid Mishneh explains that even though leniencies may generally be taken when doubts arise concerning Rabbinic obligations, the search for chametz is an exception. The entire obligation was instituted even when there was no definite knowledge that chametz existed. Hence, even in this case, a search must be made.
Though the Shulchan Aruch (Orach Chayim 439:1) accepts the Rambam's opinion, the Ramah and the other Ashkenazic authorities make the following qualification: If the person had already nullified his chametz and if the bread was small enough for the mouse to have eaten it entirely, a second search is not required.

הלכה יא
שְׁנֵי צְבוּרִין אֶחָד שֶׁל חָמֵץ וְאֶחָד שֶׁל מַצָּה וּשְׁנֵי בָּתִּים אֶחָד בָּדוּק וְאֶחָד שֶׁאֵינוֹ בָּדוּק וּבָאוּ שְׁנֵי עַכְבָּרִים זֶה נָטַל חָמֵץ וְזֶה נָטַל מַצָּה וְאֵין יָדוּעַ לְאֵי זֶה בַּיִת נִכְנַס זֶה שֶׁנָּטַל הֶחָמֵץ. וְכֵן שְׁנֵי בָּתִּים בְּדוּקִין וּצְבוּר אֶחָד שֶׁל חָמֵץ וּבָא עַכְבָּר וְנָטַל וְאֵין יָדוּעַ לְאֵיזֶה בַּיִת נִכְנַס. אוֹ שֶׁיָּדַע שֶׁנִּכְנַס לְאֶחָד מֵהֶן וְנִכְנַס אַחֲרָיו וּבָדַק וְלֹא מָצָא כְּלוּם אוֹ שֶׁבָּדַק וּמָצָא כִּכָּר. אוֹ שֶׁהָיוּ תִּשְׁעָה צְבוּרִין שֶׁל מַצָּה וְאֶחָד שֶׁל חָמֵץ וּפֵרַשׁ כִּכָּר מֵהֶן וְאֵין יָדוּעַ אִם חָמֵץ אִם מַצָּה וּבָא עַכְבָּר וְנָטַל הַכִּכָּר שֶׁפֵּרַשׁ וְנִכְנַס לְבַיִת בָּדוּק בְּכָל אֵלּוּ אֵינוֹ צָרִיךְ לִבְדֹּק פַּעַם שְׁנִיָּה שֶׁאֵין כָּאן קָבוּעַ:
כסף משנה
11.
There were two piles: one of chametz and one of matzah, and two houses: one that had been searched and one that had not been searched. Two mice came; one took chametz and one took matzah [and they entered the houses] without our knowing which house the mouse holding the chametz entered...1In such an instance, we presume that the mouse holding the chametz entered the unchecked house, and the mouse holding the matzah entered the checked house. Comparable decisions are found in Hilchot Terumah 13:14, Hilchot Issurei Biyah 9:29 and Hilchot Mikvaot 10:3.
Pesachim 10a emphasizes that this leniency is only rendered because once a person has nullified ownership over his chametz, the search is only a question of Rabbinic law. The Shulchan Aruch HaRav (Orach Chayim 439:4) agrees to this principle, but offers an addition leniency: Even if the owner did not nullify his chametz, a second search is not required when the bread the mouse was holding is small enough to be eaten at once.

Similarly, there were two houses which had been checked, with one pile of chametz before them. A mouse took [from the pile and entered a house]. However, we do not know which house he entered...2Each of the homes is judged individually. Since we do not definitely know that chametz was not brought into either of the homes, we need not change our original presumption and consider each one as free of chametz.
Hilchot Sha'ar Avot HaTum'ah 19:2 mentions a similar case, but reaches a more stringent conclusion. Leniency is only offered when the two people in question approach the Rabbis separately. If they come together, the case is judged more severely.
The Maggid Mishneh and the Kessef Mishneh both note this matter and explain that since the search for chametz is a question of Rabbinic law, greater leniency can be taken. Nevertheless, the Ramah (Orach Chayim 439:2) and other Ashkenazic authorities do not accept this decision and require a second search, should the owners of both homes approach the court together.

or we saw which one he entered, a person followed him, checked [for chametz], and did not find anything...3Pesachim 10a compares this to a case in which a corpse was presumed to be found in a field. Though Rabbi Meir maintains that the field is considered ritually impure until the corpse is found, the halachah follows the Sages, who maintain that all that is necessary is to carry out a thorough search. The Shulchan Aruch HaRav (Orach Chayim 439:6) states that this law applies even when the owner of the house had not nullified his chametz, and the search is required by Torah law.
or he checked and found bread...4we presume that this was the bread the mouse had taken. Pesachim 10a compares this to a case where a field was suspected to contain a grave; the field was searched, and a grave discovered. Though Rabbi Shimon ben Gamliel requires the entire field to be searched, Rabbi Yehudah HaNasi maintains that no further search must be made.
The Shulchan Aruch HaRav (ibid.) emphasizes that this leniency should only be followed when the owner of the house has nullified or can still nullify the ownership over his chametz. Otherwise, he must thoroughly search the entire house.

Similarly, when there were nine piles of matzah and one of chametz, and a loaf became separated from the piles, and we do not know whether it was chametz or matzah: If a mouse took the loaf that became separated and entered the house that had been checked:
In5The passage from Pesachim 9b concerning the ten butcher shops quoted in the commentary on the previous halachah, continues:[If meat from these shops] is found, follow the majority.The principle of קבוע - judging the permitted and forbidden substances as if they were equal - applies only when the doubt concerning the identity of the substance arises in the place where the presence of the forbidden substance has become fixed. Thus, since the meat has become separated (פירש) from its original place, this principle no longer applies and, as in most cases of mixtures, the decision depends on whether there is a greater number of kosher or non-kosher stores.
Similarly, in the case at hand: Since the loaf became separated from the piles before being taken by the mouse, there is no question of a prohibited substance having a fixed identity (קבוע). Hence, we follow the majority, and thus do not require a further search. The Shulchan Aruch HaRav and the Mishnah Berurah emphasize that this leniency applies even if the owner of the house had not nullified the ownership over his chametz.
all of these cases, there is no need to check a second time,6The Kessef Mishneh emphasizes that this is a complete thought in its own right. because the presence of the forbidden substance is not fixed.7According to the Kessef Mishneh, this statement applies only to the final instance mentioned in the halachah as explained.

הלכה יב
הִנִּיחַ הֶחָמֵץ בְּזָוִית זוֹ וּמְצָאוֹ בְּזָוִית אַחֵר אוֹ שֶׁהִנִּיחַ תֵּשַׁע חַלּוֹת וּמָצָא עֶשֶׂר. אוֹ שֶׁבָּא עַכְבָּר וְנָטַל הֶחָמֵץ וְסָפֵק נִכְנַס לְבַיִת זֶה אוֹ לֹא נִכְנַס. בְּכָל אֵלּוּ צָרִיךְ לִבְדֹּק:
כסף משנה
12.
A person who placed chametz in one corner and discovered it in another...1Pesachim 10b explains that the Sages felt that it was likely that the chametz discovered was not the chametz lost. Rather, different chametz was placed in the other corner, and the first chametz, deposited elsewhere throughout the house. Hence, a new search is required (See also Hilchot Mitamei Mishkav U'Moshav 12:16.)
The Shulchan Aruch HaRav (Orach Chayim 439:9) states that if the same amount of chametz that was lost is found there is no need to search further if the owner had already nullified the ownership over his chametz. The Mishnah Berurah grants an even greater leniency and frees the owner of the necessity to search, without placing any qualifications on the chametz discovered, as long as he has nullified his chametz.

or who put aside nine loaves and found ten...2Pesachim 10a compares this to the following case: "A person put aside 100 dinars of money designated as ma'aser sheni (the second tithe, to be used only to purchase food in Jerusalem) and discovered two hundred."
In Hilchot Ma'aser Sheni 6:3, the Rambam declares that none of the money is considered as ma'aser sheni. In both instances, we suppose that the substance put aside was taken away and a new substance substituted for it. Accordingly, the Magen Avraham emphasizes that the owner cannot cease his search until he finds nine piles of chametz. This law applies even if the owner has nullified his ownership over the original nine piles of chametz.

or a mouse came and took the chametz, and there is a doubt whether he entered this house or not...3Pesachim 10a likens this to a case when a person traveled through a valley in which one of the fields was known to possess a grave. Though he is unsure of whether he entered the field containing the grave or not, he must consider himself ritually impure (See Hilchot Sha'ar Avot HaTum'ah 20:9.)
The Ra'avad's text of the Mishneh Torah contained an additional clause:or there were nine piles of chametz and one pile of matzah: A loaf became separated from them and it is not known whether it was chametz or matzah. A mouse came and took it into a checked house.The Kessef Mishneh rejects the inclusion of this clause because in the previous halachah, the Rambam had already stated that once a substance is separated from its original place, its identity is determined on the basis of the majority.

In all these cases, he must search [the house again].

הלכה יג
נִכְנַס עַכְבָּר לְבַיִת וְכִכָּר בְּפִיו וְיָצָא עַכְבָּר מִשָּׁם וְכִכָּר בְּפִיו אוֹמְרִים הוּא הָרִאשׁוֹן שֶׁנִּכְנַס הוּא הָאַחֲרוֹן שֶׁיָּצָא וְאֵינוֹ צָרִיךְ לִבְדֹּק. הָיָה הָרִאשׁוֹן שֶׁנִּכְנַס שָׁחוֹר וְזֶה שֶׁיָּצָא לָבָן צָרִיךְ לִבְדֹּק. נִכְנַס עַכְבָּר וְכִכָּר בְּפִיו וְיָצְאתָה מִשָּׁם חֻלְדָּה וְכִכָּר בְּפִיהָ צָרִיךְ לִבְדֹּק. יָצָאת מִשָּׁם חֻלְדָּה וְעַכְבָּר וְכִכָּר בְּפִיהָ אֵינוֹ צָרִיךְ לִבְדֹּק שֶׁזֶּה הַכִּכָּר הוּא שֶׁהָיָה בְּפִי הָעַכְבָּר. נָחָשׁ שֶׁנִּכְנַס לְחוֹר וּפַת בְּפִיו אֵין חַיָּב לְהָבִיא חֲבָּר לְהוֹצִיאוֹ:
כסף משנה
13.
A mouse entered a house with a loaf1of chametz in its mouth. Afterwards, a mouse left there with a loaf in its mouth; we presume that the same mouse who entered originally was the one which ultimately left, and [the owner] need not search [again].2The Pri Chadash (Orach Chayim 438:1) follows this decision even when the owner did not nullify his chametz. The Shulchan Aruch HaRav follows his opinion, though the Tur requires the owner to nullify his chametz or search. If the first mouse which entered was black and the one which left was white,3Obviously, the mouse which left is not the same as the mouse that entered, and it is not likely that one mouse took the chametz from the other (Pesachim 10b). Hence, he must search [again].4even if he has already nullified his chametz (Pri Chadash, Shulchan Aruch HaRav).
If a mouse entered with a loaf in its mouth and a weasel left there with a loaf in its mouth, he must search [again].5Even though it is possible that the weasel took the chametz from the mouse, that probability is not strong enough to free the owner from the obligation to search (Pesachim, ibid.). This applies even if he nullifies his chametz (Pri Chadash, Shulchan Aruch HaRav). If a weasel left there with a mouse and a loaf in its6the weasel's mouth, he does not have to search [again].7Even though one might say that unless the chametz is found in the mouse's mouth, we cannot be sure that it is the same. Nevertheless, since it is possible that the mouse dropped the chametz out of fear (Pesachim ibid.) [We may presume] that this is the loaf which was in the mouse's mouth.8The Talmud left this questioned unanswered (תיקו). The Pri Chadash and the Shulchan Aruch HaRav explain that this decision applies only when the owner nullifies the ownership over his chametz. In such an instance, the question is only one of Rabbinic law (for according to Torah law, the nullification is sufficient). Hence, the Rambam chooses the more lenient opinion.
If a snake enters a hole with a loaf in its mouth, there is no obligation to bring a snakecharmer to remove it.9This question is also left unanswered by the Talmud (Pesachim, ibid.). Therefore, the Rambam again chooses the more lenient view.

הלכה יד
כְּזַיִת חָמֵץ בִּשְׁמֵי קוֹרָה מְחַיְּבִין אוֹתוֹ לְהָבִיא סֻלָּם לְהוֹרִידוֹ שֶׁפְּעָמִים יִפּל מִשְּׁמֵי קוֹרָה. הָיָה חָמֵץ בְּבוֹר אֵין מְחַיְּבִין אוֹתוֹ לְהַעֲלוֹתוֹ אֶלָּא מְבַטְּלוֹ בְּלִבּוֹ וְדַיּוֹ:
כסף משנה
14.
When chametz is [discovered] on a very high beam, [the owner] is obligated to bring a ladder1even if he must rent the ladder and remove it, for it might fall from the beam.2and the owner might come to eat it.
The Shulchan Aruch HaRav (Orach Chayim 438:11) and the Mishnah Berurah explain that this obligation applies even if:
a) generally, the owner would not have access to this beam;
b) he already nullified his ownership over the chametz.
If chametz is in a pit,3to which a person does not have easy access [the owner] is not obligated to bring it up.4The Maggid Mishneh emphasizes that a person is not allowed to store chametz in a pit. However, should chametz accidentally fall into the pit before it becomes forbidden... All that is necessary is for him to nullify [ownership over it] in his heart.5However, if he had not nullified ownership over his chametz and did not discover the chametz until after it becomes forbidden, he is obligated to remove the chametz from the pit (Mishnah Berurah).
The Tosefta (Pesachim 3:3) states: "Chametz which fell into a pit is considered as if it has been destroyed;" implying that even nullification is unnecessary. However, the Tzafnat Paneach differentiates between the two cases, explaining that our halachah refers to a pit to which a person could descend if required. In contrast, the Tosefta refers to a pit which is totally inaccessible, or accessible only with extreme difficulty. Since the owner cannot make use of his chametz, there is no necessity for him to nullify his ownership of it.

הלכה טו
כִּפַּת שְׂאוֹר שֶׁיִּחֲדָהּ לִישִׁיבָה אִם טָח פָּנֶיהָ בְּטִיט הֲרֵי זוֹ בְּטֵלָה וּמֻתָּר לְקַיְּמָהּ. בָּצֵק שֶׁבְּסִדְקֵי הָעֲרֵבָה אִם יֵשׁ כְּזַיִת בְּמָקוֹם אֶחָד חַיָּב לְבַעֵר. וְאִם לָאו אִם הָיָה עָשׂוּי לְחַזֵּק בּוֹ שִׁבְרֵי הָעֲרֵבָה אוֹ לִסְתֹּם בּוֹ נֶקֶב בָּטֵל בְּמִעוּטוֹ וְאִם לָאו חַיָּב לְבַעֵר. הָיוּ בּוֹ שְׁנֵי חֲצָאֵי זֵיתִים בִּשְׁנֵי מְקוֹמוֹת וְחוּט שֶׁל בָּצֵק בֵּינֵיהֶם רוֹאִין כּל שֶׁאִלּוּ יִנָּטֵל הַחוּט נִטָּלִין עִמּוֹ חַיָּב לְבַעֵר וְאִם לָאו אֵינוֹ צָרִיךְ לְבַעֵר:
כסף משנה
15.
A block of yeast which was designated to be used as a seat:1Generally, all prohibitions against eating forbidden foods do not apply after the food is no longer fit for human consumption. Nevertheless, additional stringencies are placed on chametz, because it may be useful as a leavening agent even if it is no longer fit to be eaten by a human being. Hence, it is not nullified until it is no longer fit even for animal consumption. (See Ra'avad, Maggid Mishneh, Kessef Mishneh Halachah 1:2.) If its surface was coated with mortar,2The Mishnah Berurah (Orach Chayim 442:42) explains that if the surface of the block is covered with mortar, it does not become forbidden even though it is still fit to be eaten. This act clearly implies that the owner no longer considered the chametz as food. it is [considered as] destroyed and we are permitted to keep it [on Pesach].3Its possession does not violate the prohibition against owning chametz.
The Taz emphasizes that only the prohibition against owning chametz is lifted. Even if the chametz is unfit for animal consumption, a person is forbidden to eat it on Pesach should he desire to do so.

The dough in the cracks of a kneading trough: If a size of an olive [of dough] exists in one place,4As mentioned in Halachah 1:1, the size of an olive is considered the minimum amount for which one is liable for the transgression of most of the Torah's prohibitions. one is obligated to destroy [the dough under all circumstances].5The Shulchan Aruch HaRav emphasizes that this applies even when one has nullified his ownership over this chametz or covered it with mortar. The size of an olive is considered as a significant amount and must be destroyed at all times. Should there be less than that amount:6of dough in one place, though there are many smaller pieces of dough throughout the kneading trough If it7the dough serves to reinforce the broken pieces of the kneading trough or to plug a hole, it is [considered] negligible8and thus, part of the kneading trough because of its minimal size.9and, therefore, need not be destroyed. If not,10If the dough does not serve a useful purpose one is obligated to destroy it.11for the obligation to search after and destroy chametz applies to all quantities of that substance, even if they are smaller than the size of an olive (Maggid Mishneh).
The Shulchan Aruch HaRav (Orach Chayim 442:28) explains that dough which has not become stuck to the cracks of the kneading trough must be removed. However, leniency may be taken regarding dough stuck in the cracks of the kneading trough, even though it does not serve a purpose. Should the owner nullify his ownership over his chametz, that dough need not be destroyed if:a) the entire kneading trough contains less than an olive size of chametz stuck to its sides;
b) the dough has become dirty and unfit for consumption.

Two [quantities of dough,12used to fill cracks in the kneading trough each] half the size of an olive were found in separate places, and a string of dough connects them:13Thus, the question is raised:Are the two considered as a single quantity, and hence obligated to be destroyed; or
Can they be considered as separate entities, and thus allowed to be kept?
We check whether the [pieces of] dough themselves are lifted up when the string of dough is picked up. If they are, one is obligated to destroy [them]. If not, one is not obligated to destroy [them].14This leniency applies only to dough that strengthens the kneading trough. Otherwise, they must be destroyed (Mishnah Berurah, Orach Chayim 442:35).

הלכה טז
בַּמֶּה דְּבָרִים אֲמוּרִים בַּעֲרֵבָה אֲבָל בְּבַיִת אַף עַל פִּי שֶׁאִם יִנָּטֵל הַחוּט אֵין נִטָּלִין עִמּוֹ חַיָּב לְבַעֵר מִפְּנֵי שֶׁפְּעָמִים מְקַבֵּץ אוֹתָן. הָיָה חֲצִי זַיִת בַּבַּיִת וַחֲצִי זַיִת בָּעֲלִיָּה. חֲצִי זַיִת בַּבַּיִת וַחֲצִי זַיִת בָּאַכְסַדְרָה. חֲצִי זַיִת בְּבַיִת זֶה וַחֲצִי זַיִת בְּבַיִת שֶׁלִּפְנִים מִמֶּנּוּ. הוֹאִיל וְאֵלּוּ הַחֲצָאֵי זֵיתִים דְּבוּקִין בַּכְּתָלִים אוֹ בַּקּוֹרוֹת אוֹ בַּקַּרְקָעוֹת אֵינוֹ חַיָּב לְבָעֵר אֶלָּא מְבַטֵּל בְּלִבּוֹ וְדַיּוֹ:
כסף משנה
16.
To what does the above1leniency apply? to [pieces of dough stuck to] a kneading trough. However, [if a similar situation is discovered] within a house,2whether the dough is used to fill cracks in the house or not one is obligated to destroy [the dough] even if, when the [connecting] thread [of dough] is lifted up, the pieces of dough are not raised up with it.3Based on this decision, whenever there is more than the size of an olive of dough in the same room, we are obligated to destroy any and all pieces of dough in the room, even if they are not connected by strings of dough. [This stringency was instituted] because the [smaller portions] may sometimes be brought together.4when the house is swept, and thus produce a quantity the size of an olive (Rashi, Pesachim 45b).
If half of an olive size [of dough] was found in a house and another half in the second storey;
or5where it would be unlikely for the two halves to come together (ibid.); if half of the size of an olive was found in a house and another half in [the adjoining] porch;
or6where there is a greater probability of the two small portions of chametz coming together if half of the size of an olive was found in a room7Generally, the word בית means "house." However, it is often used to mean "room." and another half in an inner8where the probability is even greater. room;
Since these portions of dough which are less than the size of an olive are found stuck to the walls, beams, or floors [of the house],9This is a major point of debate among the halachic authorities. Rabbenu Asher (Pesakim, Pesachim 3:2) writes that the dough need not be stuck to the walls of the house. However, the Maggid Mishneh and the Kessef Mishneh oppose that thesis. They argue that the only reason for leniency is that when the dough is stuck to the walls of the house, it is considered as part of the house and not as an entity in its own right. one is not obligated to destroy them. All that is necessary is to nullify them in one's heart.10After describing the above laws in detail, the Shulchan Aruch HaRav (Orach Chayim 442:30) concludes:The above represents the law itself. However, the Jews are holy and have customarily accepted greater stringencies upon themselves. They scrape away even the slightest amount of chametz, even if it is stuck to the walls of a home or utensil. They have accepted the stringency of scraping down all benches, chairs, and walls that have come into contact with chametz.

הלכה יז
הַמַּשְׂכִּיר בַּיִת סְתָם בְּאַרְבָּעָה עָשָׂר הֲרֵי זֶה בְּחֶזְקַת בָּדוּק וְאֵינוֹ צָרִיךְ לִבְדֹּק. וְאִם הֻחְזַק זֶה הַמַּשְׂכִּיר שֶׁלֹּא בָּדַק וְאָמְרוּ אִשָּׁה אוֹ קָטָן אָנוּ בְּדַקְנוּהוּ הֲרֵי אֵלּוּ נֶאֱמָנִין שֶׁהַכּל נֶאֱמָנִים עַל בִּעוּר חָמֵץ. וְהַכּל כְּשֵׁרִין לִבְדִיקָה וַאֲפִלּוּ נָשִׁים וַעֲבָדִים וּקְטַנִּים וְהוּא שֶׁיִּהְיֶה קָטָן שֶׁיֵּשׁ בּוֹ דַּעַת לִבְדֹּק:
כסף משנה
17.
A person who rents out a house on the fourteenth [of Nisan]:1One might suppose that the sequence of this halachah and the following halachah should be reversed. First, the Rambam should state who is obligated to search for chametz, and only then the fact that we can rely that this search was properly carried out. Indeed, Pesachim 4 and the Shulchan Aruch follows that sequence when discussing these laws.
Possibly, the Rambam's choice of sequence can be explained as follows: The motivating principle of many of the previous halachot is that once a person has nullified the ownership over his chametz, the search is merely a Rabbinic obligation. Hence, many leniencies can be taken.
Because of that same principle...
Behold, [the tenant may operate] under the presumption that it has been searched2Pesachim 4b questions whether we can rely on this presumption or not and does not arrive at a conclusion. Nevertheless, the Rambam's statements can be understood in light of the Pesakim of Rabbenu Asher. He explains that if ownership over the chametz is negated the obligation to search is only Rabbinic. When doubt arises regarding matters of Rabbinic law, the more lenient position may be accepted. and he need not search.3The Shulchan Aruch (Orach Chayim 437:2) qualifies this statement, requiring the prospective tenant to ask the owner of the house if it has been searched. However, if he cannot possibly ask the owner, he need not search the house. However, this applies only when the tenant has the opportunity to nullify his ownership over any chametz that may be found within the home.
[Furthermore,] even if we must assume that the person who rented out the house did not search [it],4and we know that before Pesach, chametz had definitely been kept within the home (Mishnah Berurah) should a woman or a minor say: "We have searched it," they are believed,5The Shulchan Aruch HaRav and the Mishnah Berurah emphasize that this law applies only if the chametz has been nullified. Otherwise, the statement of a woman or child may not be relied upon.
Generally, a woman's statements are accepted even as regards Torah prohibitions. However, an exception is made in this case because the search for chametz involves much effort. Hence, our Sages worried that perhaps a woman might state that she had made a thorough search even though she had merely made a superficial inspection (Tosefot, Pesachim 4b)
for everyone's statements are accepted with regard to the destruction of chametz.6for everyone's statements are accepted with regard to the destruction of chametz.7Everyone is acceptable to search [for chametz], even women, slaves- Tosefot (ibid.) states that slaves are believed in matters where a woman's word is accepted.
Everyone is acceptable to search [for chametz], even women, slaves, and minors.8Eruvin 58b and Ketubot 28a quote instances where a child's statements are not accepted even with regard to Rabbinic prohibitions. However, we may rely on their word regarding the search for chametz, because they are capable of performing the search. The latter applies only when the minor has sufficient understanding to search.9i.e., he has reached the age where his parents have begun to educate him about the prohibition against possessing chametz.

הלכה יח
הַמַּשְׂכִּיר בַּיִת לַחֲבֵרוֹ אִם עַד שֶׁלֹּא מָסַר לוֹ הַמַּפְתֵּחַ חָל אַרְבָּעָה עָשָׂר עַל הַמַּשְׂכִּיר לִבְדֹּק. וְאִם מִשֶּׁמָּסַר הַמַּפְתֵּחַ חָל אַרְבָּעָה עָשָׂר עַל הַשּׂוֹכֵר לִבְדֹּק. הַמַּשְׂכִּיר בַּיִת בְּחֶזְקַת שֶׁהוּא בָּדוּק וְנִמְצָא שֶׁאֵינוֹ בָּדוּק עַל הַשּׂוֹכֵר לִבְדֹּק וְאֵינוֹ מִקָּח טָעוּת. וַאֲפִלּוּ בְּמָקוֹם שֶׁבּוֹדְקִים בְּשָׂכָר שֶׁהֲרֵי מִצְוָה הוּא עוֹשֶׂה:
כסף משנה
18.
A person who rents1Different rules apply to a sale (Rabbenu Nissim). a house to a colleague: If2the beginning of the the fourteenth [of Nisan]3i.e., the night between the thirteenth and the fourteenth falls before [the landlord] gave the keys to [the tenant],4Rashi (Pesachim 4a) explains that giving the keys to the tenant represents the transfer of ownership of the house to the tenant. Whoever is the rightful owner of the property at the time the obligation to search begins must carry out this mitzvah.
However, Tosefot and most other halachic authorities explain that giving the keys does not formalize the act of transfer. Thus, the Maggid Mishneh explains that in this instance, the rental agreement has been concluded beforehand. Nevertheless, since the landlord is still in possession of the keys, the tenant is not able to conduct the search. Hence, the responsibility becomes that of the landlord.
the landlord is responsible for searching.5He is required to undertake this search, even though he has abandoned ownership over any chametz that might be left in the house and does not violate the prohibitions against possessing chametz because of it (Shulchan Aruch HaRav 437:1). If the fourteenth falls after the keys have been transferred,6Based on the statements of Rabbenu Nissim and the Maggid Mishneh, the Shulchan Aruch (Orach Chayim 437:1) states that this applies only once the rental agreement has been formalized through an acceptable kinyan (act of contract). However, the Mishnah Berurah mentions other opinions that require a search even if the tenant has not formalized the rental agreement. the tenant is responsible for checking.7Even though the chametz was left by the landlord, when the tenant takes over the landlordship of the house, he becomes the owner of all its contents, including the chametz.
When a person rents out a house under the presumption that it has been searched and [later, the tenant] discovers that it has not been searched,8If the landlord is available, the tenant must ask him whether the house has been searched or not. [the tenant] is responsible for searching it9He must carry out the mitzvah even though he made an explicit condition requiring the landlord to do so. and [cannot nullify the transaction by claiming that it was carried out] under false premises.10Under certain conditions, a person can nullify a business agreement on the grounds that it was carried out under false premises. This applies even when it is customary11in that locale to hire people to search, since, behold, he is performing a mitzvah.12Pesachim 4b explains that the need for searching the house is not the real factor motivating him to retract his agreement, because every Jew desires to perform mitzvot, even if doing so requires financial expense.
Based on the Maggid Mishneh, the Ramah (Orach Chayim 437:3) requires the landlord to reimburse the tenant if it is customary to hire people to search. After all, the house was rented with the explicit condition that it had been searched.

הלכה יט
הַמְפָרֵשׁ בַּיָּם וְהַיּוֹצֵא בְּשַׁיָּרָא תּוֹךְ שְׁלֹשִׁים יוֹם זָקוּק לִבְדֹּק. קֹדֶם שְׁלֹשִׁים יוֹם אֵינוֹ צָרִיךְ לִבְדֹּק. וְאִם דַּעְתּוֹ לַחֲזֹר קֹדֶם הַפֶּסַח צָרִיךְ לִבְדֹּק וְאַחַר כָּךְ יֵצֵא שֶׁמָּא יַחֲזֹר עֶרֶב הַפֶּסַח בֵּין הַשְּׁמָשׁוֹת וְלֹא יִהְיֶה לוֹ פְּנַאי לְבַעֵר. וְאִם אֵין דַּעְתּוֹ לַחֲזֹר אֵין צָרִיךְ לִבְדֹּק. וְכֵן הָעוֹשֶׂה בֵּיתוֹ אוֹצָר. תּוֹךְ שְׁלֹשִׁים יוֹם זָקוּק לִבְדֹּק וְאַחַר כָּךְ כּוֹנֵס אוֹצָרוֹ לְתוֹכוֹ. קֹדֶם שְׁלֹשִׁים יוֹם אִם דַּעְתּוֹ לְפַנּוֹתוֹ קֹדֶם הַפֶּסַח צָרִיךְ לִבְדֹּק וְאַחַר כָּךְ עוֹשֵׂהוּ אוֹצָר. וְאִם אֵין דַּעְתּוֹ לְפַנּוֹתוֹ קֹדֶם הַפֶּסַח אֵינוֹ צָרִיךְ לִבְדֹּק:
כסף משנה
19.
A person who sets out to sea or one who leaves in a caravan within thirty days [of Pesach] is obligated to search1Furthermore, any chametz which he knows about must be removed from his possession (Magen Avraham, Orach Chayim 436:1. [for chametz].2at night by candlelight before he departs (Magen Avraham). However, no blessing is recited (Shulchan Aruch).
The Shulchan Aruch emphasizes that this law applies only when a person does not leave anyone else at home (e.g., a wife or older child) who could conduct the search at the customary time.
[If he leaves] before thirty days [prior to Pesach],3Thirty days before Pesach, we begin "asking and explaining the laws of the holiday." Hence, from that time onward, concern is shown for all the Pesach laws (Pesachim 6a). he is not obligated to search. However, if he intends to return before Pesach,4Even if his intention is to return far before Pesach, if there is a likelihood that his return may be delayed until the holiday, he must search before departing (Chatam Sofer). he must search before departing,5even if he departs at the beginning of the year (Pesachim 6a). lest he [be delayed and] return Pesach eve at nightfall,6The Shulchan Aruch HaRav and the Mishnah Berurah maintain that this law applies only when the person is going on a sea voyage or caravan where delay is a frequent phenomenon. A person who sets out on a sure land journey is not obligated to search before he departs. when he will have no opportunity to destroy [the chametz].7As stated in Halachah 1:9, the prohibitions against possessing chametz begin after the conclusion of the fifth hour on the fourteenth of Nisan. From that time onward, it is forbidden to nullify any chametz that we possess. However, if he does not intend to return,8until after Pesach he does not have to search.9Nevertheless, he is obligated to nullify any chametz that might be in his possession on Pesach eve. This nullification takes effect even though he is very far from the chametz in his home (Ramah, Magen Avraham).
Similarly, a person who makes his house a storage room:10chametz which is buried under more than three handbreadths of other substances is considered as having been removed from a person's property and need not be uncovered and destroyed before Pesach. (See Halachah 3:11.) Thus, making the house a storeroom and covering any chametz with more than that amount of other material would free him from the obligation of searching (Rashi, Pesachim 6a).
However, the Sages explain that this leniency applies only to chametz which accidentally becomes covered by other substances.
If he does so11intentionally covering the chametz with other goods within thirty days [of Pesach], he is required to search and then bring in the goods he wants to store.12Once the thirty-day period when the Pesach laws begin to be studied arrives, one is obligated to search. Over thirty days before Pesach: If he intends to remove the goods before Pesach, he is required to search13The Kessef Mishneh (and the Shulchan Aruch) quote certain opinions that do not obligate a search, explaining that it is far less likely that the person will be delayed in removing his goods and bring about a situation where he will uncover the chametz on Passover eve. and then bring in the goods he wants to store; if he does not intend to remove the goods before Pesach, he does not have to search.14The Mishnah Berurah (437:15) explains that most authorities allow this leniency only when the owner has only a suspicion, but no definite knowledge of chametz. However, if he definitely knows that chametz is found under the goods, the chametz must be removed. Nevertheless, there are some opinions that do not require the removal of chametz whose existence is known.

זמנים הלכות חמץ ומצה פרק ב
Zemanim Hametz and Matza Chapter 2