Halacha

הלכה א
בּוֹעֵל נִדָּה כְּנִדָּה שֶׁהוּא אָב מֵאֲבוֹת הַטֻּמְאָה שֶׁל תּוֹרָה מְטַמֵּא כֵּלִים בְּמַגָּע וּמְטַמֵּא אָדָם בְּמַשָּׂא וּבְמַגָּע וּמְטַמֵּא בְּהֶסֵּט וּמְטַמֵּא מִשְׁכָּב וּמֶרְכָּב כְּנִדָּה:
כסף משנה
1.
A person who has intimate relations with a nidah is impure like she is. He is one of the primary sources of impurity according to Scriptural Law. He imparts impurity to keilim by touching them and imparts impurity to people through carrying, touching, and moving, and he imparts impurity to the surface on which he lies or rides like a nidah does.

הלכה ב
אֵין מִשְׁכַּב בּוֹעֵל נִדָּה וּמֶרְכָּבוֹ כְּמִשְׁכַּב נִדָּה וּמֶרְכָּבָהּ שֶׁהַמִּשְׁכָּב אוֹ הַמֶּרְכָּב שֶׁדָּרְסָה עָלָיו נִדָּה אָב מֵאֲבוֹת הַטֻּמְאָה וּמִשְׁכַּב בּוֹעֵל נִדָּה וּמֶרְכָּבוֹ וְלַד טֻמְאָה כְּכֵלִים שֶׁנּוֹגֵעַ בָּהֶן שֶׁאֵינָן מְטַמְּאִין אָדָם וְלֹא כֵּלִים אֶלָּא אֳכָלִין וּמַשְׁקִין בִּלְבַד. וְלָמָּה נִגְרְעָה טֻמְאַת מִשְׁכָּבוֹ מִטֻּמְאַת מִשְׁכָּבָהּ מִפְּנֵי שֶׁנֶּאֱמַר בְּבוֹעֵל נִדָּה (ויקרא טו כד) "וּתְהִי נִדָּתָהּ עָלָיו וְטָמֵא שִׁבְעַת יָמִים" וְנֶאֱמַר בּוֹ (ויקרא טו כד) "כָּל הַמִּשְׁכָּב אֲשֶׁר יִשְׁכַּב עָלָיו יִטְמָא" מֵאַחַר שֶׁנֶּאֱמַר וּתְהִי נִדָּתָהּ עָלָיו אֵינִי יוֹדֵעַ שֶׁהוּא מְטַמֵּא מִשְׁכָּב וְלָמָּה נֶאֱמַר. מִפִּי הַשְּׁמוּעָה לָמְדוּ שֶׁהַכָּתוּב נִתְּקוֹ מִטֻּמְאָה חֲמוּרָה מִלְּטַמֵּא אָדָם וְכֵלִים וּתְלָאוֹ בְּטֻמְאָה קַלָּה שֶׁיִּהְיֶה מִשְׁכָּבוֹ וָלָד וְלֹא יְטַמֵּא אָדָם וְכֵלִים אֶלָּא אֳכָלִין וּמַשְׁקִין בִּלְבַד כִּשְׁאָר וַלְדוֹת הַטֻּמְאוֹת:
כסף משנה
2.
The status of the impurity imparted by a man who was intimate with a nidah to a surface on which one lies or rides is not the same as that imparted by a nidah to a surface on which one lies or rides. For a surface on which one lies or rides that was stepped on by a nidah is a primary source of ritual impurity. In contrast, a surface on which one lies or rides that was stepped on by a man who was intimate with a nidah is a derivative of ritual impurity like keilim that he touched which do not impart impurity to other people or to other keilim, only to foods and liquids.
Why is the impurity that he imparts of a lesser status than the impurity that she imparts? Because with regard to a man who was intimate with a nidah, Leviticus 15:24 states: "Her nidah impurity will be imparted to him and he will be impure for seven days" and continues: "Any surface on which he lies shall be impure." Now, since it is stated: "Her nidah impurity will be imparted to him," would it not be obvious that he imparts impurity to a surface on which one lies? Why then was it stated? According to the Oral Tradition, it was taught that the Torah removed it from the severe category of impurity in which it imparts impurity to people and keilim and placed it in a lesser category in which a surface on which he lies is a derivative and does not impart impurity to people and keilim, only to foods and liquids like other derivatives of impurity.

הלכה ג
אֶחָד הַבָּא עַל הַנִּדָּה אוֹ עַל שׁוֹמֶרֶת יוֹם כְּנֶגֶד יוֹם אוֹ עַל הַיּוֹלֶדֶת [בֵּין כְּדַרְכָּן בֵּין שֶׁלֹּא כְּדַרְכָּן] אֶחָד הַמְעָרֶה וְאֶחָד הַגּוֹמֵר בֵּין גָּדוֹל שֶׁבָּא עַל הַקְּטַנָּה בֵּין קָטָן שֶׁבָּא עַל הַגְּדוֹלָה מִתְטַמֵּא מִשּׁוּם בּוֹעֵל נִדָּה. בַּמֶּה דְּבָרִים אֲמוּרִים כְּשֶׁהָיָה הַבּוֹעֵל בֶּן תֵּשַׁע שָׁנִים וְיוֹם אֶחָד וְהַנִּבְעֶלֶת הָיְתָה בַּת שָׁלֹשׁ שָׁנִים וְיוֹם אֶחָד. אֲבָל פָּחוֹת מִכָּאן אֵינוֹ מִתְטַמֵּא מִשּׁוּם בּוֹעֵל נִדָּה אֶלָּא מִשּׁוּם נוֹגֵעַ בְּנִדָּה בִּלְבַד שֶׁהוּא וָלָד וְאֵינוֹ אָב. וְכֵן בּוֹעֵל הַזָּב הֲרֵי הוּא כְּנוֹגֵעַ בּוֹ וְאֶחָד הַנּוֹגֵעַ בְּזָב אוֹ הַנִּבְעֶלֶת מִן הַזָּב:
כסף משנה
3.
A man contracts the impurity of one who is intimate with a nidah or a zavah when he is intimate with such a woman or if he is intimate with a woman who is watching one day because of a day of impurity, or a woman after childbirth, whether the two engaged in vaginal or anal intercourse, whether he inserted only the corona or inserted the entire male organ, and whether it was an adult male who was intimate with a minor or a male minor who was intimate with an adult woman.
When does the above apply? When the male involved is at least nine years old and the woman involved at least three years old. If, however, either is younger than this, the male does not contract the impurity of one who has relations with a nidah, only that of one who touches a woman in the nidah state. His impurity is thus considered a derivative; he is not a primary source. Similarly, one who sodomizes a zav is considered as one who touches a zav. Also, the same laws that apply to one who touches a zav apply to a woman who is intimate with such a person.

הלכה ד
הַנִּדָּה וְהַזָּבָה וְשׁוֹמֶרֶת יוֹם כְּנֶגֶד יוֹם וְהַיּוֹלֶדֶת אַף עַל פִּי שֶׁלֹּא רָאֲתָה דָּם כֻּלָּם מְטַמְּאוֹת לְמַפְרֵעַ מֵעֵת לְעֵת אוֹ מִפְּקִידָה לִפְקִידָה וְזֶהוּ הַנִּקְרָא מֵעֵת לְעֵת שֶׁבְּנִדָּה. כֵּיצַד. אִשָּׁה שֶׁהָיְתָה טְהוֹרָה וְאֵין לָהּ וֶסֶת וּבָדְקָה עַצְמָהּ בְּשַׁחֲרִית וּמָצְאָה טְהוֹרָה וּבַחֲצִי הַיּוֹם בָּדְקָה עָצְמָה וּמָצְאָה דָּם הֲרֵי כָּל הַטָּהֳרוֹת שֶׁעָשְׂתָה מִשְּׁעַת פְּקִידָה רִאשׁוֹנָה עַד שְׁעַת פְּקִידָה שְׁנִיָּה טְמֵאוֹת לְמַפְרֵעַ. וְכֵן אִם בָּדְקָה הַיּוֹם וּמָצְאָה טְהוֹרָה וּלְאַחַר שְׁנַיִם אוֹ שְׁלֹשָׁה יָמִים בָּדְקָה וּמָצְאָה דָּם כָּל הַטָּהֳרוֹת שֶׁעָשְׂתָה מֵעֵת שֶׁבָּדְקָה וּמָצְאָה דָּם עַד כ''ד שָׁעוֹת טְמֵאוֹת לְמַפְרֵעַ. וְעֵד שֶׁלְּאַחַר הַתַּשְׁמִישׁ הֲרֵי הוּא כִּפְקִידָה וְשֶׁלִּפְנֵי הַתַּשְׁמִישׁ אֵינוֹ כִּפְקִידָה מִפְּנֵי שֶׁאֵינָהּ בּוֹדֶקֶת בּוֹ יָפֶה:
כסף משנה
4.
All of the following - nidah, a zavah, a woman who is watching one day because of a day of impurity, or a woman after childbirth even if she did not experience uterine bleeding - contract impurity retroactively for a twenty-four hour period or until the last vaginal inspection the woman made. This is referred to as the twenty-four period of a nidah.
What is implied? A woman who did not have a fixed time when she would menstruate was pure. She made a vaginal inspection in the morning and found that she was pure. At noon, she made another vaginal inspection and discovered blood. Accordingly, any ritually pure entities that she touched between the first inspection and the second inspection are impure retroactively. Similarly, if she made a vaginal inspection one day and found herself pure and made another inspection two or three days afterwards and discovered uterine bleeding, all of the articles she touched within twenty-four hours before the inspection during which she discovered the bleeding are considered as impure retroactively.
A checking cloth used after intimacy is considered as a vaginal inspection, but one used before intimacy is not, because she does not make a thorough inspection with it.

הלכה ה
אִשָּׁה שֶׁיֵּשׁ לָהּ וֶסֶת וְרָאֲתָה דָּם בִּשְׁעַת וֶסְתָּהּ דַּיָּהּ שְׁעָתָהּ וְאֵינָהּ טְמֵאָה לְמַפְרֵעַ. הִגִּיעַ שְׁעַת וֶסְתָּהּ וְלֹא בָּדְקָה עַצְמָהּ וּלְאַחַר יָמִים בָּדְקָה עַצְמָהּ וּמָצְאָה דָּם הֲרֵי זוֹ טְמֵאָה לְמַפְרֵעַ וַהֲרֵי הִיא בְּחֶזְקַת נִדָּה מִשְּׁעַת וֶסְתָּהּ. וְזוֹ הִיא טֻמְאַת וֶסְתּוֹת הָאֲמוּרָה בְּכָל מָקוֹם. וְאִם מָצְאָה עַצְמָהּ טְהוֹרָה כְּשֶׁבָּדְקָה אַחַר הַוֶּסֶת הֲרֵי זוֹ טְהוֹרָה:
כסף משנה
5.
A woman who has a fixed time when she menstruates and discovers uterine bleeding at that time is impure only from that time onward. She is not impure retroactively. If the fixed time when she menstruates arrives and she did not inspect herself and then inspected herself after the passage of several days and discovered uterine bleeding, she is considered as impure retroactively and is assumed to be a nidah from the fixed time that she usually menstruates. This is the impurity associated with the fixed time for menstruation referred to universally.
If the woman discovered that she was pure when she inspected herself after her fixed time for menstruation, she is pure.

הלכה ו
כָּל אִשָּׁה שֶׁיֵּשׁ לָהּ וֶסֶת תַּרְגִּישׁ בְּעַצְמָהּ. מְפַהֶקֶת. אוֹ מִתְעַטֶּשֶׁת. אוֹ חוֹשֶׁשֶׁת פִּי כְּרֵסָהּ וְשִׁפּוּלֵי מֵעֶיהָ. אוֹ אֲחָזָהּ צַמְרוּרִית. אוֹ רֹאשָׁהּ כָּבֵד עָלֶיהָ אוֹ אֵיבָרֶיהָ כְּבֵדִין וְכַיּוֹצֵא בְּאֵלּוּ. וְיֵשׁ אִשָּׁה שֶׁדַּרְכָּהּ לִרְאוֹת בְּעֵת שֶׁיַּתְחִיל בָּהּ מִקְרֶה אֶחָד מֵאֵלּוּ מִיָּד בִּתְחִלָּתוֹ וְיֵשׁ אִשָּׁה שֶׁתַּמְתִּין בְּמִקְרֶה זֶה שָׁעָה אוֹ שְׁתַּיִם וְאַחַר כָּךְ תִּרְאֶה הַדָּם בְּסוֹף הַוֶּסֶת. הָיְתָה לְמוּדָה לִהְיוֹת רוֹאָה בִּתְחִלַּת הַוֶּסֶת כָּל הַטָּהֳרוֹת שֶׁעָשְׂתָה בְּתוֹךְ הַוֶּסֶת טְמֵאוֹת. הָיְתָה לְמוּדָה לִהְיוֹת רוֹאָה בְּסוֹף הַוֶּסֶת כָּל הַטָּהֳרוֹת שֶׁעָשְׂתָה בְּתוֹךְ הַוֶּסֶת טְהוֹרוֹת. וְאֵינָהּ חוֹשֶׁשֶׁת אֶלָּא מִשָּׁעָה שֶׁדַּרְכָּהּ לִרְאוֹת עַד עֵת שֶׁמָּצְאָה דָּם:
כסף משנה
6.
Whenever a woman has a fixed time during which she menstruates, she will also experience physical symptoms at the onset of menstruation, e.g., she will yawn, sneeze, feel heaviness and strain at the opening to her stomach and lower body, become overcome by trembling, or feel that her head and limbs are heavy, or the like.
There are women whose pattern is to experience bleeding immediately after one of these physical symptoms begins. And there are other women who will wait, and continue experiencing these symptoms for an hour or two and experience bleeding only at the end of the expected time. When a woman's pattern is to experience bleeding at the beginning of the expected time, any pure articles she touches during the expected time are impure. If her pattern is to experience bleeding at the end of the expected time, any pure articles she touches during the expected time are pure. She is only concerned about the articles she touched from the time she is accustomed to experience bleeding until she actually discovers bleeding.

הלכה ז
הָרוֹאֶה כֶּתֶם טְמֵאָה לְמַפְרֵעַ עַד עֵת הַפְּקִידָה. וְכֵן הַבֶּגֶד שֶׁנִּמְצָא עָלָיו הַכֶּתֶם טָמֵא לְמַפְרֵעַ. וְעַד כַּמָּה. עַד שֶׁתֹּאמַר בָּדַקְתִּי הֶחָלוּק הַזֶּה וְלֹא הָיָה עָלָיו כֶּתֶם. אֲפִלּוּ כִּבְּסַתּוּ וְלֹא בְּדָקַתּוּ טָמֵא מִקֹּדֶם הַכִּבּוּס לְמַפְרֵעַ עַד שְׁעַת בְּדִיקָה. וַאֲפִלּוּ נִמְצָא הַכֶּתֶם לַח הֲרֵי זֶה מְטַמֵּא לְמַפְרֵעַ עַד שְׁעַת הַבְּדִיקָה שֶׁאֲנִי אוֹמֵר מִיָּמִים הָיָה שָׁם וְעַתָּה נָפְלוּ עָלָיו מַיִם וְנַעֲשָׂה לַח:
כסף משנה
7.
When a woman discovers a bloodstain, she is retroactively impure until the time she made an inspection. Similarly, a garment on which a stain was discovered is retroactively impure.
Until when? Until such a time concerning which the woman says: "I checked this garment and it did not have a bloodstain." Even if she washed the garment, but did not inspect it, it is impure retroactively from before she washed it until the time when it was inspected. Even if a moist stain was found, she is considered impure retroactively until the time she made an inspection. The rationale is that there is reason to say that it was there previously and now water fell upon it and caused it to become moist.

הלכה ח
וְכָל הַנָּשִׁים שֶׁדַּיָּן שְׁעָתָן כִּתְמָן כִּרְאִיָּתָן וְאֵינוֹ מְטַמֵּא אוֹתָן לְמַפְרֵעַ. כָּל אֵלּוּ הַנָּשִׁים הַטְּמֵאוֹת לְמַפְרֵעַ בֵּין רָאֲתָה דָּם בֵּין מָצָאתָה כֶּתֶם מְטַמְּאוֹת מִשְׁכָּב וּמֶרְכָּב לְמַפְרֵעַ לְטַמֵּא אָדָם וּבְגָדִים. וְכֵן רֻקָּן וּמֵימֵי רַגְלֵיהֶן טְמֵאִין לְמַפְרֵעַ. וַאֲפִלּוּ כְּלִי חֶרֶשׂ הַמֻּקָּף צָמִיד פָּתִיל מְטַמְּאוֹת אוֹתָן לְמַפְרֵעַ. אֲבָל אֵינָן מְטַמְּאוֹת אֶת הַבּוֹעֵל לְמַפְרֵעַ מִשּׁוּם בּוֹעֵל נִדָּה אֶלָּא מִשּׁוּם נוֹגֵעַ בִּלְבַד. אֲבָל הָרוֹאָה כֶּתֶם הַבּוֹעֵל אוֹתָהּ מֵאַחַר שֶׁנִּמְצֵאת הַכֶּתֶם טָמֵא מִשּׁוּם בּוֹעֵל נִדָּה:
כסף משנה
8.
A bloodstain discovered by any of the women who are impure only from the time they discover uterine bleeding onward is equivalent to the discovery of uterine bleeding and does not cause her to contract impurity retroactively.
Any of the women who contract impurity retroactively, whether they discovered uterine bleeding or a bloodstain, also impart impurity retroactively to surfaces upon which one lies or rides, causing them to impart impurity to a person or to garments. Similarly, their saliva and urine impart impurity retroactively. They even impart impurity retroactively to an earthenware container that is sealed closed.
They do not, however, impart the severe impurity associated with intimacy with a nidah to a man who is intimate with them. He is considered only as if he touched them. Whenever a woman discovers a bloodstain, a man who is intimate with her after she discovered the stain is considered impure as one who was intimate with a nidah.

הלכה ט
מְעֻבֶּרֶת שֶׁהוֹצִיא הָעֻבָּר אֶת יָדוֹ וְהֶחֱזִירָהּ אִמּוֹ טְמֵאָה לֵדָהּ. וְטֻמְאַת יוֹלֶדֶת (י''ד) וְטֻמְאַת מֵעֵת לְעֵת אוֹ מִפְּקִידָה לִפְקִידָה לְמַפְרֵעַ כְּמוֹ שֶׁבֵּאַרְנוּ וְטֻמְאַת וְסָתוֹת וְטֻמְאַת כְּתָמִים הַכּל מִדִּבְרֵי סוֹפְרִים וְטֻמְאָתָן מִסָּפֵק לְפִיכָךְ אֵין שׂוֹרְפִין עֲלֵיהֶן תְּרוּמָה וְקָדָשִׁים אֶלָּא תּוֹלִין. וְכֵן חֻלִּין שֶׁנַּעֲשׂוּ עַל טָהֳרַת הַקֹּדֶשׁ שֶׁנִּטְמְאוּ בְּאֵלּוּ תּוֹלִין. אֲבָל הַנַּעֲשִׂים עַל טָהֳרַת הַתְּרוּמָה וְחֻלִּין הַטְּבוּלִין לְחַלָּה אֵין מִתְטַמְּאִין בְּכָל אֵלּוּ הַטֻּמְאוֹת שֶׁהֵן מִדִּבְרֵיהֶן. נִמְצֵאתָ אוֹמֵר שֶׁכָּל אַחַת מֵאֵלּוּ הַנָּשִׁים וּמִשְׁכָּבָן וּמֶרְכָּבָן וְרֻקָּן וּמֵימֵי רַגְלֵיהֶן וּבוֹעֵל רוֹאָה כֶּתֶם מֵאַחַר שֶׁנִּמְצָא הַכֶּתֶם וּבוֹעֵל יוֹלֶדֶת מֵאַחַר שֶׁיָּצָא הָאֵיבָר וְחָזַר כֻּלָּן אֲבוֹת טֻמְאוֹת מִדִּבְרֵי סוֹפְרִים:
כסף משנה
9.
When a fetus sticks out his hand from the womb of a pregnant woman, his mother contracts the impurity of a woman who gave birth.
The impurity of a woman whose fetus sticks out its hand, the impurity imposed retroactively for 24 hours or until the previous inspection that was mentioned, the impurity associated with the fixed time when a woman usually menstruates, and the ritual impurity associated with bloodstains are all Rabbinic decrees and were instituted because of a doubt. Therefore terumah and sacrificial foods are not burnt because of them. Instead, the ruling concerning them is held in abeyance. Similarly, the ruling concerning ordinary foods that were treated with the sanctity associated with sacrificial foods that contracted impurity from one of these sources is held in abeyance. Nevertheless, ordinary food that is treated with the sanctity associated with terumah and ordinary food from which challah has not yet been separated do not contract impurity from any of these sources, for they are Rabbinic decrees.
Thus one can conclude that: all of these women mentioned previously in this halachah, an object on which one lies or rides to which they imparted impurity, their saliva, their urine, one who is intimate with a woman who discovered a bloodstain after the bloodstain was discovered, one who was intimate with a woman after the fetus stuck out a limb and then returned it, are all primary sources of impurity according to Rabbinic decree.

טהרה הלכות מטמאי משכב ומושב פרק ג
Taharah Metamei Mishkav and Moshav Chapter 3