Yichud Sources and application

Kidushin 80b MISHNA: A man may not be secluded with two women lest he sin with them, but one woman may be secluded with two men. Rabbi Shimon says: Even one man may be secluded with two women when his wife is with him, and in that situation he may even sleep in the same inn with two women, because his wife guards him from sinning with them. They further said that a man may be secluded with his mother, and with his daughter, and sleep alongside them with bodily contact without clothes, since there is no concern that they will engage in sexual intercourse. And when they, the son or daughter, have grown up, this one sleeps in her garment and that one sleeps in his garment, but they may share a bed.

The Gemara asks: From where are these matters, that it is prohibited for a man to be secluded with women, derived? Rabbi Yoḥanan says in the name of Rabbi Yishmael: From where is there an allusion from the Written Torah to the prohibition against seclusion? As it is stated concerning one who incites others to idolatrous worship: “If your brother, the son of your mother, entices you” (Deuteronomy 13:7). The Gemara asks: From where are these matters, that it is prohibited for a man to be secluded with women, derived? Rabbi Yoḥanan says in the name of Rabbi Yishmael: From where is there an allusion from the Written Torah to the prohibition against seclusion? As it is stated concerning one who incites others to idolatrous worship: “If your brother, the son of your mother, entices you” (Deuteronomy 13:7). The Gemara asks: From where are these matters, that it is prohibited for a man to be secluded with women, derived? Rabbi Yoḥanan says in the name of Rabbi Yishmael: From where is there an allusion from the Written Torah to the prohibition against seclusion? As it is stated concerning one who incites others to idolatrous worship: “If your brother, the son of your mother, entices you” (Deuteronomy 13:7). The Gemara comments: Shall we say the mishna is not in accordance with the opinion of Abba Shaul, as it is taught in a baraita: If a child dies any time during the first thirty days after his birth, he is not given a proper funeral but is carried out held in their bosom, not on a bier, and buried by one woman and two men. But he may not be buried by one man and two women, due to the prohibition against seclusion. Abba Shaul says: He may even be buried by one man and two women. This indicates that Abba Shaul deems it permitted for a man to be secluded with two women. The Gemara comments: Shall we say the mishna is not in accordance with the opinion of Abba Shaul, as it is taught in a baraita: If a child dies any time during the first thirty days after his birth, he is not given a proper funeral but is carried out held in their bosom, not on a bier, and buried by one woman and two men. But he may not be buried by one man and two women, due to the prohibition against seclusion. Abba Shaul says: He may even be buried by one man and two women. This indicates that Abba Shaul deems it permitted for a man to be secluded with two women

The verse relates that after Amnon raped her: “And Tamar put ashes on her head and rent her garment of many colors that was on her” (II Samuel 13:19). The Sages taught in the name of Rabbi Yehoshua ben Korḥa: Tamar established a great fence at that time by way of her public outcry, as people said: If such an occurrence could happen to the daughters of kings, all the more so could it happen to the daughters of ordinary people. If such an occurrence could happen to modest women like Tamar, who resisted, all the more so could it happen to licentious women. Rav Yehuda says that Rav says: At that time they decreed about seclusion, that a man should not be secluded with women who are forbidden to him, and about a single woman. The Gemara objects: Seclusion with a woman forbidden by familial ties is prohibited by Torah law, and was not a rabbinic decree issued in the time of David. As Rabbi Yoḥanan says in the name of Rabbi Shimon ben Yehotzadak: From where is there an allusion to the halakha that seclusion is forbidden by Torah law? As it is stated: “If your brother, the son of your mother, entices you” (Deuteronomy 13:7). One can ask: But does the son of a mother entice, and does the son of a father not entice? Why mention only the son of a mother? Rather, this verse serves to tell you that only a son may be secluded with his mother. Sons are frequently with their mother, and two half-brothers of one mother consequently have the opportunity to grow close to one another. But another individual may not be secluded with those with whom relations are forbidden by the Torah, including a stepmother. Therefore, half-brothers of one father spend less time together.

the prohibition on Yichud is from the Torah

When the incident concerning Amnon and Tamar occurred, David and his court decreed a prohibition against entering into privacy with an unmarried woman. Although an unmarried woman is not an ervah, such an act is considered as entering into privacy with an ervah. Shammai and Hillel decreed a prohibition against entering into privacy with gentilesץ

Thus when anyone enters into privacy with a woman, whether Jew or gentile, with whom such an act is forbidden, both the man and the woman are given stripes for rebellious conduct and an announcement is made concerning them. An exception is made with regard to a married woman. Although it is forbidden to enter into privacy with her, if one does enter into privacy with her, corporal punishment is not administered lest a rumor be initiated that she committed adultery. Thus a rumor might spread that her children are mamzerim.

One woman should not enter into privacy even with many men unless the wife of one of them is present. Similarly, one man should not enter into privacy even with many women, But when there are many women together with many men, we do not show concern for the prohibition against entering into privacy.

If the men were outside and the women were inside or if the men were inside and the women were outside, and one woman - or one man - separated themselves and joined the group of the other sex, the prohibition against entering into privacy applies.

Even a man whose business and profession [brings him into contact] with women is forbidden to enter into privacy with them. What should he do? He should involve himself with them while accompanied by his wife or turn to another profession.

One woman may not be in seclusion even with many men, unless the wife of one of the men is present. And similarly, one man may not be in seclusion even with many women. Note: And there are those who say that a woman may seclude herself with two "good men" [of fit morals] when in-town. And men are to be considered as good men, generally. But if they are "steeped" [in sexual immorality], it's forbidden to be secluded even with ten of them. And all this [applies] when in-town. However, in the field, or during the night even in-town, three men are required to be there, even if they are "good men". And there are those who permit one man with many women, if his business is not [primarily] involved with women.