Halacha

הלכה א
שְׁנַּיִם שֶׁנֶּאֶסְרָה הֲנָאַת כָּל אֶחָד מֵהֶן עַל חֲבֵרוֹ בֵּין בְּנֵדֶר בֵּין בִּשְׁבוּעָה הֲרֵי אֵלּוּ מֻתָּרִין לְהַחְזִיר אֲבֵדָה זֶה לָזֶה מִפְּנֵי שֶׁהוּא מִצְוָה. וּבְמָקוֹם שֶׁדַּרְכָּן שֶׁנּוֹטֵל שָׂכָר הַמַּחֲזִיר אֶת הָאֲבֵדָה יִפּל הַשָּׂכָר לַהֶקְדֵּשׁ. שֶׁאִם יִטּל שָׂכָר נִמְצָא נֶהֱנֶה וְאִם לֹא יִטּוֹל נִמְצָא מְהַנֶּה:
כסף משנה
1.
When two people are forbidden - by vow or by oath - to derive benefit from each other, they are allowed1And since they are allowed, they are obligated. to return a lost article to each other, because doing so is a mitzvah.2For he is not returning it as a favor to him, but instead, in fulfillment of the Torah's command [the Rambam's Commentary to the Mishnah (Nedarim 4:2). In a place where it is customary for the person who returns a lost article to receive a reward, the reward should be given to the Temple treasury.3Or, in the present age, to charity. This is preferable to destroying it. For if [the person who returns the lost article] will take the reward, he will be receiving benefit.4I.e., he will be returning it for the sake of the reward and not for the sake of the mitzvah (ibid.). If he does not take it, he will be giving the other person benefit.5For ordinarily the person would pay a reward for the return of the lost article.

הלכה ב
וּמֻתָּרִין בִּדְבָרִים שֶׁהֵם בְּשֻׁתָּפוּת כָּל יִשְׂרָאֵל. כְּגוֹן הַר הַבַּיִת (וְהַלְּשָׁכוֹת) וְהָעֲזָרוֹת וְהַבְּאֵר שֶׁבְּאֶמְצַע הַדֶּרֶךְ. וַאֲסוּרִין בִּדְבָרִים שֶׁהֵם בְּשֻׁתָּפוּת כָּל אַנְשֵׁי הָעִיר כְּגוֹן הָרְחָבָה שֶׁבָּעִיר וְהַמֶּרְחָץ וּבֵית הַכְּנֶסֶת וְהַתֵּבָה וְהַסְּפָרִים:
כסף משנה
2.
They are [both] permitted [to make use of] those entities that are owned jointly by the entire Jewish people,6Technically, the other person has a share in these places, for they are owned communally. Nevertheless, since each person's individual share is so small, these places are considered as if they are ownerless and not as communal property (see ibid. 5:4). e.g., the Temple Mount, its chambers, its courtyards, and a well in the midst of a highway.7I.e.., a well built for the pilgrims' journey to Jerusalem from Babylon for the pilgrimage festivals (ibid.). They are forbidden [to make use of] those entities that are owned jointly by all the inhabitants of that city,8For in this instance, each person's share is greater and more distinct.
The Ramban and the Ran object to the Rambam's ruling, maintaining that this ruling does not apply with regard to an entity like a synagogue that cannot be divided. In such an instance, it is considered as a communal entity and the person who took the vow is allowed to make use of it. The Shulchan Aruch (Yoreh De'ah 224:1) quotes both views. See the Lechem Mishneh and the Turei Zahav 224:1 who elaborate in support of the Rambam's position.
e.g., its marketplace, its bathhouse, its synagogue, its ark, and its holy texts.

הלכה ג
וְכֵיצַד יַעֲשׂוּ כְּדֵי שֶׁיִּהְיוּ מֻתָּרִין בִּדְבָרִים אֵלּוּ. כָּל אֶחָד וְאֶחָד מִשְּׁנֵיהֶם כּוֹתֵב חֶלְקוֹ לַנָּשִׂיא אוֹ לְאֶחָד מִשְּׁאָר הָעָם וּמְזַכֶּה לוֹ בְּחֶלְקוֹ עַל יְדֵי אַחֵר. וְנִמְצָא כָּל אֶחָד מֵהֶם כְּשֶׁיִּכָּנֵס לַמֶּרְחָץ שֶׁהוּא לְכָל אַנְשֵׁי הָעִיר אוֹ לְבֵית הַכְּנֶסֶת אֵינוֹ נִכְנָס לִרְשׁוּת חֲבֵרוֹ אֶלָּא לִרְשׁוּת אֲחֵרִים שֶׁהֲרֵי כָּל אֶחָד מֵהֶם נִסְתַּלֵּק מֵחֶלְקוֹ שֶׁבְּמָקוֹם זֶה וּנְתָנוֹ בְּמַתָּנָה:
כסף משנה
3.
What can they do so that they will be permitted to use these entities? Each one of them should sign over his portion to the nasi9The leader of the Jewish people. He is mentioned, because it is very unlikely that he will forbid a member of the people from using his property (Nedarim 48a). or to another person and have him acquire that portion through the medium of another person.10I.e., the person acquiring the portion need not know about his acquisition. We follow the principle that a person can acquire property without his knowledge if it is to his benefit to do so (see Hilchot Zechiyah UMatanah 4:2). Thus when either of them enter a bathhouse belonging to all the members of the city or to the synagogue, he is not entering the property of the colleague [from whom he is forbidden to benefit], for each of them has relinquished his share of the place and given it away as a present.

הלכה ד
הָיוּ שְׁנֵיהֶם שֻׁתָּפִין בְּחָצֵר. אִם יֵשׁ בָּהּ דִּין חֲלוּקָה הֲרֵי אֵלּוּ אֲסוּרִין לְהִכָּנֵס לָהּ עַד שֶׁיַּחֲלֹקוּ וְיִכָּנֵס כָּל אֶחָד לְחֶלְקוֹ. וְאִם אֵין בָּהּ דִּין חֲלוּקָה כָּל אֶחָד וְאֶחָד נִכְנָס לְבֵיתוֹ וְהוּא אוֹמֵר בְּתוֹךְ שֶׁלִּי אֲנִי נִכְנָס. וּבֵין כָּךְ וּבֵין כָּךְ שְׁנֵיהֶם אֲסוּרִים לְהַעֲמִיד רֵחַיִם וְתַנּוּר וּלְגַדֵּל תַּרְנְגוֹלִין בְּחָצֵר זוֹ:
כסף משנה
4.
[The following laws apply when] they are both partners in a courtyard.11In the Talmudic era, it was common that several houses would open up to a courtyard that was the combined property of the homeowners. In this halachah, we are speaking of an instance where two of those homeowners took vows forbidding them to benefit from each other. If it can be divided,12See Hilchot Shechenim 2:1 which states that if after the division of a courtyard, each of the homeowners will receive a plot of land four cubits by four cubits as his individual property, the courtyard should be divided if one of the neighbors requests that this be done. they are forbidden to enter it unless it is divided and each person enters his portion. If it cannot be divided,13I.e., if it were to be divided, the homeowners would not receive a portion of land that size. each one should enter his house, saying: "I am entering my property."14Rabbenu Nissim explains this ruling based on the principle of bereirah, i.e., retroactively, it becomes apparent that when he enters the courtyard, he is entering property that was designated as his. We are forced to accept this definition (even though generally, the principle of bereirah is not followed in questions of Scriptural Law), for there is no alternative in this instance. The person has a right to the courtyard and he cannot be forbidden from using his own property. See Siftei Cohen 226:4, Turei Zahav 226:1. Regardless,15Whether it cannot be divided or whether it can be divided, but was not divided yet. they are both forbidden to place a mill or an oven there or to raise chickens in this courtyard.16Bava Batra 57b relates that partners in a courtyard have the right to prevent each other from performing such activities. Although most partners do not exercise this right, in this instance, by failing to exercise the right, one is providing benefit to the other person (Rabbenu Nissim).

הלכה ה
שְׁנַיִם שֶׁהָיוּ שֻׁתָּפִין בְּחָצֵר וְנָדַר אֶחָד מֵהֶן שֶׁלֹּא יְהַנֶּה בּוֹ הַשֵּׁנִי כּוֹפִין אֶת הַנּוֹדֵר לִמְכֹּר חֶלְקוֹ. נָדַר שֶׁלֹּא יֵהָנֶה הוּא בַּשֵּׁנִי הֲרֵי זֶה מֻתָּר לְהִכָּנֵס לְבֵיתוֹ מִפְּנֵי שֶׁבִּרְשׁוּתוֹ הוּא נִכְנָס. אֲבָל אֵינוֹ יָכוֹל לְהִשְׁתַּמֵּשׁ בַּחָצֵר כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
5.
When two people are partners in a courtyard17I.e., a courtyard to small for the owners to divide. and one of them takes an oath that the other may not benefit from him, we force the person who took the oath to sell his portion.18His vow imposes unnecessary hardship on the other person who has a legitimate right to the property. Hence, we compel him to sell his share of the courtyard rather than put his colleague in a situation where he might transgress.
If he took an oath not to benefit from the other person, he is permitted to enter his home, for he is entering his own domain.19The Shulchan Aruch (Yoreh De'ah 226:2) states that the person who took the vow is forbidden to enter the courtyard. The rationale is that the Rambam's understanding is accepted, except that an additional stringency is applied, lest the person remain in the courtyard for other purposes besides entering and departing his home (Siftei Cohen 226:10). He may not, however, make any other use of the courtyard, as explained [in the previous halachah].20We do not force him to sell his portion of the courtyard because he is causing difficulty only to himself and he is willing to abide by his prohibition (Radbaz).
The Ra'avad objects to the Rambam's ruling, citing Nedarim 46a as support for his understanding. He mentions that the Jerusalem Talmud (Nedarim 5:2) appears to support the Rambam's interpretation, but states that we should abide by the principle that whenever there is a difference of opinion between the Babylonian and Jerusalem Talmuds, the perspective of the Babylonian Talmud should be followed. See the Radbaz and the Kessef Mishneh who try to reconcile the differences in the positions of the two Talmuds. As mentioned, the Shulchan Aruch follows the Rambam's understanding, but is even more stringent.

הלכה ו
הָיָה אֶחָד מִן הַשּׁוּק אָסוּר בַּהֲנָאַת אֶחָד מִשְּׁנֵיהֶם. הֲרֵי זֶה מֻתָּר לְהִכָּנֵס לֶחָצֵר. מִפְּנֵי שֶׁהוּא אוֹמֵר לוֹ לְתוֹךְ שֶׁל חֲבֵרְךָ אֲנִי נִכְנָס אֵינִי נִכְנָס לְתוֹךְ שֶׁלְּךָ:
כסף משנה
6.
If a person from outside was forbidden to benefit from either of [the owners of the courtyard],21This is speaking about a courtyard that is too small to require division (Radbaz). he may enter the courtyard,22The Shulchan Aruch (Yoreh De'ah 226:1) states that this applies only when the other owner of the courtyard needs that person. Otherwise, he is forbidden to enter. for he tells [the person from whom he is forbidden to benefit]: "I am entering your colleague's domain, not yours."

הלכה ז
מִי שֶׁאָסַר הֲנָיַת אֻמָּה מִן הָאֻמּוֹת עַל עַצְמוֹ. הֲרֵי זֶה מֻתָּר לִקַּח מֵהֶן בְּיוֹתֵר וְלִמְכֹּר לָהֶן בְּפָחוֹת. אָסַר הֲנָיָתוֹ עֲלֵיהֶם אִם שׁוֹמְעִין לוֹ שֶׁיִּקַּח מֵהֶן בְּפָחוֹת וְיִמְכֹּר בְּיוֹתֵר מֻתָּר. וְאֵין גּוֹזְרִין כָּאן שֶׁלֹּא יִמְכֹּר גְּזֵרָה שֶׁמָּא יִקַּח. שֶׁהֲרֵי לֹא נָדַר מֵאִישׁ אֶחָד כְּדֵי שֶׁנִּגְזֹר עָלָיו [אֶלָּא] מֵאֻמָּה כֻּלָּהּ. שֶׁאִם אִי אֶפְשָׁר לוֹ לִשָּׂא וְלִתֵּן עִם זֶה יִשָּׂא וְיִתֵּן עִם אַחֵר. לְפִיכָךְ אִם אָסַר הֲנָיָתָן עָלָיו הֲרֵי זֶה מַשְׁאִילָן וּמַלְוֶה אוֹתָן. אֲבָל לֹא יִשְׁאַל מֵהֶם וְלֹא יִלְוֶה מֵהֶן:
כסף משנה
7.
When a person forbids himself from benefiting from one of the nations, he is permitted to buy [an article] from them at more than the market price and sell to them at less than the market price.23For thus he is suffering a loss every time he deals with them. If he forbids them from benefiting from him, if they are willing, it is permitted for him to purchase from them for less than the market price and sell to them at more than the market price.24For they are suffering a loss every time they deal with him. We do not issue a decree forbidding him to sell [at less than the market price], lest he purchase [at less than the market price].25As a decree was made with regard to an individual. See Chapter 6, Halachah 16. [The rationale is that] he did not take a vow concerning only one individual, in which instance such a decree would be appropriate, but concerning an entire nation and if it is impossible for him to do business with one person, he will do business with another.26I.e., with regard to one individual, there is room for stringency, but this stringency is not required with regard to an entire nation, for there is (Radbaz). Therefore, if he forbade himself from benefiting from them, he may lend both articles and money to them, but may not borrow either of these from them.27I.e., we do not make a decree like we do with regard to an individual (Siftei Cohen 227:7).

הלכה ח
אָסַר הֲנָיָתוֹ עֲלֵיהֶן וַהֲנָיָתָן עָלָיו לֹא יִשָּׂא וְיִתֵּן עִמָּהֶם. וְכֵן לֹא יִשְּׂאוּ הֵן וְיִתְּנוּ עִמּוֹ וְלֹא יַשְׁאִיל לָהֶן וְלֹא יִלְוֶה מֵהֶם וְלֹא יַלְוֶה אוֹתָן:
כסף משנה
8.
If he forbade them from benefiting from him and himself from benefiting from them, he should not do business with them, nor may they do business with him.28For one of them, either they or he will be benefiting from the sale. He may not borrow an article from them or lend an article to them, nor borrow money from them or lend money from them.

הלכה ט
אָסַר עַל עַצְמוֹ הֲנָיַת בְּנֵי הָעִיר אָסוּר לְהִשָּׁאֵל עַל נִדְרוֹ לְחָכָם מִבְּנֵי אוֹתָהּ הָעִיר (הַהִיא). וְאִם נִשְׁאַל וְהִתִּיר לוֹ הֲרֵי נִדְרוֹ מֻתָּר כְּמוֹ שֶׁבֵּאַרְנוּ:
כסף משנה
9.
If he forbade himself from benefiting from the inhabitants of a city, he is forbidden to ask the sage of the city for the repeal of his vow.29For this is a benefit that he is receiving. If, however, he did ask him and he released the vow, the vow is released, as explained.30For when a sage releases a vow, it is as if it never existed. Hence, it is as if he were never forbidden to approach the sage. See Chapter 4, Halachah 13, and notes.

הלכה י
מִי שֶׁאָסַר הֲנָיַת הַבְּרִיּוֹת עָלָיו הֲרֵי זֶה מֻתָּר לֵהָנוֹת בְּלֶקֶט שִׁכְחָה וּפֵאָה וּמַעֲשַׂר עָנִי הַמִּתְחַלֵּק בָּגֳרָנוֹת אֲבָל לֹא בְּתוֹךְ הַבַּיִת:
כסף משנה
10.
When a person forbade himself from benefiting from any other people, he is permitted to derive benefit from leket, shichechah, pe'ah31Leket refers to crops that drop from a reaper's hand in the field. He is forbidden to pick them up again, but instead must leave them for the poor (Leviticus 19:10 . Shichechah refers to crops or bundles forgotten in the field by accident. The harvesters may not return and collect, but must instead leave them for the poor (Deuteronomy 24:19 . Pe'ah refers to a corner of the field which must be left unharvested, so that it could be harvested by the poor (Leviticus 19:9 . See Hilchot Matanot Aniyim chs. 1,4, and 5 where these mitzvot are discussed. and the tithe for the poor that is distributed in the granaries,32In the third year of the six-year agricultural, instead of taking the second tithe to be eaten in Jerusalem in a state of holiness, it is given to the poor (Deuteronomy 14:28; Hilchot Matanot Aniyim ch. 6). The person who took the vow is allowed to benefit from these crops, because the owner of the field is not considered as giving him anything of his own. Instead, he is fulfilling a mitzvah. but not that [which is distributed] from one's home.33Nedarim 83-84a explains this distinction. When the tithe for the poor is distributed in the granaries, it may be taken by a poor person without asking. The owner does not have the right to decided to whom he will give it. If, however, he has already brought produce from the tithe for the poor home, he has the right to choose to whom to give it.

הלכה יא
מִי שֶׁאָסַר הֲנָיָתוֹ עַל הַכֹּהֲנִים וְעַל הַלְוִיִּם הֲרֵי אֵלּוּ בָּאִין וְנוֹטְלִין מַתְּנוֹתֵיהֶם עַל כָּרְחוֹ. וְאִם אָמַר כֹּהֲנִים אֵלּוּ וּלְוִיִּם אֵלּוּ הֲרֵי אֵלּוּ אֲסוּרִין. וְיִתֵּן תְּרוּמוֹתָיו וּמַעַשְׂרוֹתָיו לְכֹהֲנִים וּלְוִיִּם אֲחֵרִים. וְהוּא הַדִּין בְּמַתְּנוֹת עֲנִיִּים עִם הָעֲנִיִּים:
כסף משנה
11.
When a person forbade priests or Levites from benefiting from his property, they may come and take the gifts [to be separated from his produce]34I.e., the tithes that must be given to the Levites and terumah which must be given to the priests. against his will.35Since he is obligated to give these presents to the priests and Levites, he has no choice in the matter and must make these gifts. Generally, a person is allowed to decide which Levite and which priest, he desires to give these gifts to. In this instance, however, since he forbade all priests from benefiting from his property, there is no one to whom he can give it. Hence his right to decide is taken from him and any priest or Levite can come and take the portions.
If he says: "These priests and these Levites [are forbidden to benefit from my property,]" they are bound by the prohibition.36Since the terumah and tithes may be given to others, there is no reason to take away the person's right to distribute them as he desires, for that right is of financial value (Nedarim 84b). He should give his terumah and tithes to other priests and Levites. Similar laws apply with regard to the gifts for the poor37E.g., those mentioned in the previous halachah. See Siftei Cohen 227:9 and Turei Zahav 227:3 who rule that this concept also applies with regard to charity. and the poor.

הלכה יב
מִי שֶׁהָיְתָה הֲנָיָתוֹ אֲסוּרָה עַל חֲבֵרוֹ וְאֵין לַחֲבֵרוֹ מַה יֹּאכַל. הוֹלֵךְ אֵצֶל הַחֶנְוָנִי וְאוֹמֵר אִישׁ פְּלוֹנִי אָסוּר בַּהֲנָיָתִי וְאֵינִי יוֹדֵעַ מָה אֶעֱשֶׂה. אִם הָלַךְ הַחֶנְוָנִי וְנָתַן לוֹ וּבָא וְנָטַל מִזֶּה הֲרֵי זֶה מֻתָּר:
כסף משנה
12.
When it is forbidden for a person to benefit a colleague and that colleague has nothing to eat, the person may go to a storekeeper and say: "So-and-so is forbidden to benefit from me and I don't know what to do."38The Shulchan Aruch (Yoreh De'ah 221:8) is even more lenient and states that he may say: "Anyone who sustains so-and-so will not suffer a loss," for he is still merely intimating that one should support him. He may not say: "Whoever hears my voice should sustain so-and-so," for that it a direct command. Nor may he tell one person: "If you sustain so-and-so, you will not suffer a loss," for then it appears as if he is appointing him as an agent for this purpose. It is permitted for the storekeeper to go and give [food] to the colleague and take [payment] from that person.39Since the person did not charge the storekeeper with providing the colleague with food, he is not responsible for the account [Rama (Yoreh De'ah 221:8)]. If he, nevertheless, chooses to pay it, he is not considered to have given benefit to that colleague.

הלכה יג
הָיָה בֵּיתוֹ לִבְנוֹת גְּדֵרוֹ לִגְדֹּר שָׂדֵהוּ לִקְצֹר וְהָלַךְ אֵצֶל פּוֹעֲלִים וְאָמַר אִישׁ פְּלוֹנִי אָסוּר בַּהֲנָיָתִי וְאֵינִי יוֹדֵעַ מָה אֶעֱשֶׂה. וְהָלְכוּ הֵן וְעָשׂוּ עִמּוֹ וּבָאוּ לָזֶה וְנָתַן לָהֶן שְׂכָרָן הֲרֵי זֶה מֻתָּר. שֶּׁנִּמְצָא זֶה שֶׁפָּרַע לוֹ חוֹבוֹ. וּכְבָר בֵּאַרְנוּ שֶׁזֶּה מֻתָּר לִפְרֹעַ לוֹ חוֹבוֹ:
כסף משנה
13.
[Similar laws apply]40The Kessef Mishneh states that the two instances are not entirely analogous, for the first involves providing the person with food necessary for his livelihood, while the second involves the performance of a task that is important, but not vital for him. Perhaps this is the reason why in the preceding halachah, the Rambam stated: "The person may go to a storekeeper," i.e., he is permitted as an initial and preferred option. In this halachah, by contrast, he states: "If the person... approached workers," i.e., the Rambam is describing a law that applies after the fact, but not initially. if it is necessary to build [that colleague's] house, put up a fence for him, or harvest his field. If the person from whom it was forbidden to benefit approached workers and told them: "So-and-so is forbidden to benefit from me and I don't know what to do,"41The Radbaz explains that although the previous law was mentioned, it is also necessary to state this law, because it is uncommon for workers to extend credit on money do them. This is, by contrast, a common practice for storekeepers. They may then perform these activities, go back to that person, and he may pay them. For he is paying the debt of the colleague and we already explained42Chapter 6, Halachah 4. that a person [from whom one is forbidden to benefit] may pay a debt for his colleague.

הלכה יד
הָיוּ מְהַלְּכִין בַּדֶּרֶךְ וְאֵין לוֹ מַה יֹּאכַל. נוֹתֵן לְאַחֵר מִשּׁוּם מַתָּנָה וְהַלָּה מֻתָּר בָּהּ. וְאִם אֵין עִמָּהֶם אַחֵר מַנִּיחַ עַל הַסֶּלַע וְאוֹמֵר הֲרֵי הֵן מֻפְקָרִין לְכָל מִי שֶׁיַּחְפֹּץ וְהַלָּה נוֹטֵל וְאוֹכֵל:
כסף משנה
14.
If the two43I.e., a person who took a vow not to benefit from a person and that person. were traveling on a journey and [the person who is forbidden to benefit from his colleague] does not have anything to eat, [that colleague] may give [food] to another person as a present and [the person who is forbidden] is then permitted to partake of it.44Giving a present is not permitted in the situations described in the previous halachot, because there are other alternatives. Hence it is considered as too great a leniency. In this situation, there is no other alternative and therefore it is permitted. See Siftei Cohen 221:52. If there is no one else with them, [the person whose property is forbidden] should put [food] on a stone and say: "This [food] is considered ownerless for everyone who desires it."45Generally, according to Rabbinic Law, there must be three people present when an object is declared ownerless. In this instance, however, since there is no other alternative, we do not require anything more than required by Scriptural Law (Siftei Cohen 221:53). The other person may then take it and eat.46For then he is not partaking of the property of the person from whom he is forbidden to benefit, but from ownerless property.

הלכה טו
נָתַן לְאֶחָד מַתָּנָה וְאָמַר לוֹ הֲרֵי סְעֻדָּה זוֹ נְתוּנָה לְךָ מַתָּנָה וְיָבוֹא פְּלוֹנִי שֶׁהוּא אָסוּר בַּהֲנָיָתִי וְיֹאכַל עִמָּנוּ הֲרֵי זֶה אָסוּר. וְלֹא עוֹד אֶלָּא [אֲפִלּוּ] אִם נָתַן לוֹ סְתָם וְחָזַר וְאָמַר לוֹ רְצוֹנְךָ שֶׁיָּבוֹא פְּלוֹנִי וְיֹאכַל עִמָּנוּ. אִם הוֹכִיחַ סוֹפוֹ עַל תְּחִלָּתוֹ שֶׁלֹּא נָתַן לוֹ אֶלָּא עַל מְנָת שֶׁיָּבוֹא פְּלוֹנִי וְיֹאכַל אָסוּר. כְּגוֹן שֶׁהָיְתָה סְעֻדָּה גְּדוֹלָה וְהוּא רוֹצֶה שֶׁיָּבוֹא אָבִיו אוֹ רַבּוֹ וְכַיּוֹצֵא בָּהֶן לֶאֱכל מִסְּעוּדָתוֹ. שֶׁהֲרֵי סְעוּדָתוֹ מוֹכַחַת עָלָיו שֶׁלֹּא גָּמַר לְהַקְנוֹת לוֹ. וְכֵן כָּל כַּיּוֹצֵא בָּזֶה:
כסף משנה
15.
If, [however,] he gives a colleague a present [of a feast] and tells him: "This feast is given to you as a present. Let so-and-so who is forbidden to benefit from me come and eat with us," this is forbidden.47For he is obviously making this gift solely so that the other person may partake of it. If it is a large feast, it is obvious that a person is not preparing it for the sake of giving it to a colleague. Nedarim 48b gives as an example, an instance where a person's father was forbidden to benefit from him. When he made a wedding feast for his son, he tried to employ this tactic to enable his father to attend. Moreover, even if he gave the present without saying anything, but afterwards48The Kessef Mishneh states that there are opinions that maintain that this law applies only when the statements were made immediately after giving the feast. The wording chosen by the Rambam, however, indicates that the law applies even if he makes the statements later. The interpretation of the Kessef Mishneh is borne out by the Rambam's Commentary to the Mishnah (Nedarim 5:5). said: "Do you want so-and-so to come and eat with us?" it is forbidden if it appears that initially, he gave the present solely so that ultimately so-and-so could eat with them. For example, it is a large feast and he wants his father, his teacher, or the like to partake of the feast. For [the size of] the feast indicates that he did not intend to give it to him. Similar laws apply in all analogous situations.

הלכה טז
כָּל מַתָּנָה שֶׁאִם הִקְדִּישָׁהּ לֹא תִּהְיֶה מֻקְדֶּשֶׁת אֵינָהּ מַתָּנָה. וְכָל הַנּוֹתֵן לָזֶה מַתָּנָה עַל מְנָת לְהַקְנוֹתָהּ לְאַחֵר הֲרֵי זֶה הָאַחֵר קָנָה בְּעֵת שֶׁיַּקְנֶה לוֹ הָרִאשׁוֹן. וְאִם לֹא הִקְנָה לוֹ הָרִאשׁוֹן לְאוֹתוֹ אַחֵר לֹא קָנָה לֹא הָרִאשׁוֹן וְלֹא הַשֵּׁנִי:
כסף משנה
16.
Any present that, were it to be consecrated [by the recipient], the consecration would not be effective, is not considered as a present.49I.e., the giver tells the recipient: "I did not give you the present so that you could consecrate it."
Nedarim, loc. cit., states this principle in continuation of the above story. After the son gave the wedding feast to a colleague so that his father could attend, that colleague consecrated it. When the giver, protested saying that he had not given it to him for that purpose, the recipient complained that he was not going to serve as a medium to allow the first person to break his vow. When the Sages were asked to rule about this situation, they stated the principle mentioned by the Rambam here.

Whenever a person gives a colleague a present with the stipulation that he transfer it to another person, that other person acquires ownership at the time the first [recipient] transfers it to him.50I.e., we do not say that since the first recipient is going to give to the second, the second acquires it when it is acquired by the first. This is not a situation where the first recipient is acting as an agent for the second. Instead, he acquires it first on his own behalf and then transfers it to the other person. If the first recipient does not transfer it to that other person, neither the first, nor the second [recipient] acquires it.51The first does not acquire it, because it was given to him only on condition that it be transferred to the second. Since that condition was not fulfilled, his own acquisition is not binding (see Hilchot Zechiyah UMatanah 3:6). The second person does not acquire it, because ownership was never transferred to him.

הלכה יז
מִי שֶׁנֶּאֶסְרָה הֲנָיָתוֹ עַל בַּעַל בִּתּוֹ וְהוּא רוֹצֶה לָתֵת לְבִתּוֹ מָעוֹת כְּדֵי שֶׁתִּהְיֶה נֶהֱנֵית בָּהֶן וּמוֹצִיאָה אוֹתָן בַּחֲפָצֶיהָ. הֲרֵי זֶה נוֹתֵן לָהּ וְאוֹמֵר לָהּ הֲרֵי הַמָּעוֹת הָאֵלּוּ נְתוּנִין לָךְ בְּמַתָּנָה וּבִלְבַד שֶׁלֹּא יְהֵא לְבַעֲלִיךְ רְשׁוּת בָּהֶן אֶלָּא יִהְיוּ לְמַה שֶּׁאַתְּ נוֹתֶנֶת לְפִיךְ אוֹ לְמַה שֶּׁתִּלְבְּשִׁי וְכַיּוֹצֵא בָּזֶה. וַאֲפִלּוּ אָמַר לָהּ עַל מְנָת שֶׁאֵין לְבַעֲלִיךְ רְשׁוּת בָּהֶן אֶלָּא מַה שֶּׁתִּרְצִי עֲשִׂי בָּהֶן לֹא קָנָה הַבַּעַל וּמַה שֶּׁתִּרְצֶה תַּעֲשֶׂה בָּהֶן. אֲבָל אִם נָתַן לָהּ מַתָּנָה וְאָמַר לָהּ עַל מְנָת שֶׁאֵין לְבַעֲלִיךְ רְשׁוּת בָּהֶן וְלֹא פֵּרֵשׁ שֶׁתִּהְיֶה הַמַּתָּנָה הַזֹּאת לְכָךְ וּלְכָךְ אוֹ לְמַה שֶּׁתִּרְצֶה תַּעֲשֶׂה בָּהֶן הֲרֵי קָנָה אוֹתָהּ הַבַּעַל לֶאֱכל פֵּרוֹתֶיהָ. וְדָבָר זֶה אָסוּר שֶׁהֲרֵי הוּא אָסוּר בַּהֲנָיַת חוֹתְנוֹ:
כסף משנה
17.
[The following principle applies when a person's son-in-law is forbidden to benefit from him and he desires to give his daughter money so that she can benefit from it and spend it as she desires.52Ordinarily, whatever a woman acquires immediately is given to her husband's jurisdiction. While she remains the legal owner, he has the legal right to control it and use the profits as he sees fit. In this instance, this would be forbidden for the son-in-law is prohibited against benefiting from his father-in-law, as the Rambam states in the conclusion of the halachah. He should give her a present and say: "This money53If he gives her the food itself, it is not necessary to make any stipulations (Radbaz, Siftei Cohen 222:1). is given to you as a present on the condition that your husband has no authority over it.54Tosafot Yom Tov (Nedarim 11:8) states that from Hilchot Zechiyah UMatanah 3:13, it appears that the inclusion of this part of the statement is not an absolute necessity. As long as he specifies that the present is being given for a specific purpose alone, the husband does not acquire rights to it. Rav Yosef Caro does not accept this option, however, in his Kessef Mishneh and quotes the Rambam's wording from this halachah in his Shulchan Aruch (Yoreh De'ah 222:1; see Siftei Cohen 222:2). Instead, it shall be used for what you put in your mouth, what you cloth yourself, and the like."55Since the father has designated the money for a specific purpose, it may be used only for that and thus the son never acquires a right to it. The rationale is closely related to the concept of a vow. Just as a vow can determine how property may be used even after it leaves the domain of the person who took the vow, so, too, the father can determine how his property may be used even after it leaves his domain.
This ruling teaches that even though it is to the husband's benefit that his wife eats or is clothed - indeed, he is responsible to provide for these needs of hers - the husband is not considered to have benefited from this present (the Rambam's Commentary to the Mishnah, Nedarim 11:8).
Even if he said: "...on the condition that your husband has no authority over it. Instead, it shall be used for whatever you want to do with it,"56In this instance, even though the specific purpose for which the present was given was not stated at the outset, when the woman decides what she desires to do with the present, retroactively, it is as if it was given for that purpose alone.
The Ra'avad differs with the Rambam concerning this point, noting that although the law stated in the first clause is accepted by all authorities, the one stated in this clause is the subject of a difference of opinion between the Sages Rav and Shmuel in Nedarim 88b. The Rambam's ruling follows the opinion of Shmuel although generally, with regard to matters involving the Torah's prohibitions, the halachah follows that of Rav. The Radbaz and the Kessef Mishneh state that other Rishonim also follow Shmuel's perspective and give logical support for it. The Shulchan Aruch (Yoreh De'ah 222:1) quotes both views without stating which should be followed.
the husband does not acquire it and she may do what she desires with it.
If, however, he gave her a present and told her. "...on the condition that your husband has no authority over it," but did not specify the purpose for which the present was being given or even did not say that it was intended for whatever she desires, the husband acquires it to derive benefit from it.57See Hilchot Zechiyah UMatanah 3:13. The rationale is that the giver does not have the prerogative of negating the rights given the husband by the Rabbis. This would be forbidden, because he is forbidden to benefit from his father-in-law.58Nevertheless, the present is binding. The husband should purchase something that brings income with the money. That article belongs to his wife. He should give the proceeds to charity, since he is not allowed to benefit from them (Radbaz)

הפלאה הלכות נדרים פרק ז
Haflaah Nedarim Chapter 7