both are so called because each is lawful to the other. It is also said that they are so called because each resides wherever the other resides, from the sense of settling or alighting. Another explanation is that each unties the other’s waist-wrapper, from untying, the opposite of tying. (1)

In summary, the wives of a man’s sons and of his male descendants, however far removed, whether through fosterage or blood relationship, are forbidden to him by the marriage contract itself. Allah’s words, “from your own loins,” were meant to make clear that the wife of an adopted son is not forbidden to the man who adopted him. The Prophet, may Allah bless him and grant him peace, married the former wife of Zayd ibn Harithah, whom the Messenger of Allah, may Allah bless him and grant him peace, had adopted.

The fourth category of those forbidden through marriage is the wife of one’s father or grandfather, however far removed. She is forbidden to a man’s child and to his descendants by the marriage contract itself, whether the father is related through fosterage or blood relationship, as Allah, exalted is He, says: “And do not marry those women whom your fathers married.” This has already been mentioned.

Every woman rendered forbidden to a man by a marriage contract is likewise rendered forbidden through intercourse with a woman he owns or through intercourse under the mistaken belief that there was a valid marriage. Thus, if he has intercourse with a woman ⦗82/a⦘ under such a mistaken belief, or with a slave woman whom he owns, the mother and daughter of the woman with whom he had intercourse become forbidden to him; and that woman becomes forbidden to his father and his son.

If he commits fornication with a woman, the scholars differed concerning this. One group held that neither the mother nor the daughter of the woman with whom he committed fornication becomes forbidden to the fornicator, while the adulteress becomes forbidden to his father and his son. This was the view of Ali, Ibn Masud, and Ibn Abbas, may Allah be pleased with them. It was also held by Sa'id ibn al-Musayyib, Urwah, and al-Zuhri, and was adopted by Malik and al-Shafi'i, may Allah the Exalted have mercy on them.

Others held that it does establish prohibition. This was narrated from Imran ibn Husayn and Abu Hurayrah, may Allah be pleased with them, and was the view of Jabir ibn Zayd and al-Hasan, as well as the adherents of legal opinion.

If a man touches a woman lustfully or kisses her, is this treated like consummation in establishing the prohibitions of marriage affinity? Likewise, if he touches a woman lustfully, is this treated like intercourse in rendering her daughter forbidden? There are two views. The sounder view, and that of most scholars, is that it does establish prohibition. The second is that it does not, just as a lustful look does not establish it.

Allah’s words, “And that you marry two sisters at the same time”: it is not permissible for a man to be married to two sisters simultaneously, whether they are sisters through blood relationship or fosterage. If he marries a woman and then irrevocably divorces her, he may marry her sister. Similarly, if he owns two sisters, he may not have intercourse with both of them. Once he has had intercourse with one of them, he may not have intercourse with the other until he renders the first unlawful to himself.

Likewise, it is not permissible for a man to be married simultaneously to a woman and her paternal aunt, or to a woman and her maternal aunt, on account of what Abu al-Hasan al-Sarakhsi informed us,