(13) לא תנאף THOU SHALT NOT COMMIT ADULTERY — The term ניאוף, “adultery”, is technically only applicable to the case of a married woman, as it is said, (Leviticus 20:10) […the wife of his neighbour], the נואף and the נואפת shall surely be put to death”, and it further states, (Ezekiel 16:32) “The woman that comitteth adultery, that taketh strangers instead of her husband”.

(13) לא תנאף, this commandment is phrased as applying to sexual intercourse with someone else’s legal wife because this is the most likely scenario; it applies to all forbidden sexual intercourse.

(10) If a man commits adultery with a married woman, committing adultery with another man’s wife, the adulterer and the adulteress shall be put to death.

Speak to the Israelite people and say to them: If any man’s wife has gone astray and broken faith with him (13) in that a man has had carnal relations with her unbeknown to her husband, and she keeps secret the fact that she has defiled herself without being forced, and there is no witness against her— (14) but a fit of jealousy comes over him and he is wrought up about the wife who has defiled herself; or if a fit of jealousy comes over one and he is wrought up about his wife although she has not defiled herself— (15) the man shall bring his wife to the priest. And he shall bring as an offering for her one-tenth of an ephah of barley flour. No oil shall be poured upon it and no frankincense shall be laid on it, for it is a meal offering of jealousy, a meal offering of remembrance which recalls wrongdoing. (16) The priest shall bring her forward and have her stand before the LORD. (17) The priest shall take sacral water in an earthen vessel and, taking some of the earth that is on the floor of the Tabernacle, the priest shall put it into the water. (18) After he has made the woman stand before the LORD, the priest shall bare the woman’s head and place upon her hands the meal offering of remembrance, which is a meal offering of jealousy. And in the priest’s hands shall be the water of bitterness that induces the spell. (19) The priest shall adjure the woman, saying to her, “If no man has lain with you, if you have not gone astray in defilement while married to your husband, be immune to harm from this water of bitterness that induces the spell. (20) But if you have gone astray while married to your husband and have defiled yourself, if a man other than your husband has had carnal relations with you”— (21) here the priest shall administer the curse of adjuration to the woman, as the priest goes on to say to the woman—“may the LORD make you a curse and an imprecation among your people, as the LORD causes your thigh to sag and your belly to distend; (22) may this water that induces the spell enter your body, causing the belly to distend and the thigh to sag.” And the woman shall say, “Amen, amen!” (23) The priest shall put these curses down in writing and rub it off into the water of bitterness. (24) He is to make the woman drink the water of bitterness that induces the spell, so that the spell-inducing water may enter into her to bring on bitterness. (25) Then the priest shall take from the woman’s hand the meal offering of jealousy, elevate the meal offering before the LORD, and present it on the altar. (26) The priest shall scoop out of the meal offering a token part of it and turn it into smoke on the altar. Last, he shall make the woman drink the water. (27) Once he has made her drink the water—if she has defiled herself by breaking faith with her husband, the spell-inducing water shall enter into her to bring on bitterness, so that her belly shall distend and her thigh shall sag; and the woman shall become a curse among her people. (28) But if the woman has not defiled herself and is pure, she shall be unharmed and able to retain seed. (29) This is the ritual in cases of jealousy, when a woman goes astray while married to her husband and defiles herself, (30) or when a fit of jealousy comes over a man and he is wrought up over his wife: the woman shall be made to stand before the LORD and the priest shall carry out all this ritual with her. (31) The man shall be clear of guilt; but that woman shall suffer for her guilt.

1. If there are no witnesses that she committed adultery, but rather she herself says she has committed adultery, we are not concerned about this matter to forbid her [from her husband], as perhaps she [merely] set her eyes upon another.
2. This is only if there is no reason to believe her, but if there is reason to believe her, she is trusted (Decisions of Mahara"i #222). But she does lose her marriage contract--both the essence and the additions--and property which she brought into the marriage and is not longer extant.
3. If she goes back on her words and gives a reason that she would have lied in the first place, she is trusted (Glosses of Mordekhai to Kidushin).
4. If he had believed her and his thoughts are now reliant on her words, he is obligated to send her out, but we do not force him to send her out.
5. But if she were raped, she does not lose her marriage contract, whether she is the wife of an Israelite or the wife of a priest.

If one witness testified about an affair, the husband is not obligated to divorce her, even if he is believed in the eyes of the husband.

When adulterers multiplied, the ceremony of the bitter waters ceased and it was Rabban Yohanan ben Zakkai who discontinued it, as it is said, “I will not punish their daughters for fornicating, nor their daughters-in-law for committing adultery, for they themselves [turn aside with whores and sacrifice with prostitutes]” (Hosea