the wife with whom he has not consummated the marriage (5) are lawful; due to the saying of Him, the Exalted: {And if you have not entered into them, there is no sin upon you} (6). These are the stepdaughters (raba'ib), and these are not among those whose mother is prohibited. He only mentioned her because she is lawful, so her ruling might be confused. If it is said: Then why is the daughter of the stepdaughter prohibited, while the daughter of the father's wife is not prohibited? We say: Because the daughter of the stepdaughter is a stepdaughter, whereas the daughter of the wife is not a wife. And because the effective cause (illa) for the prohibition of the stepdaughter is that it is difficult to avoid looking at her and being in seclusion with her, by virtue of her being in his care in his house; and this meaning is found in her daughter even if she is a descendant. The wife was prohibited due to the father's and son's marriage to her, and this is not found in her daughter.

1150 - Issue; he said: (And sexual intercourse through an unlawful act is prohibited, just as sexual intercourse through a lawful act or through [doubt/shubha] is prohibited).

He means that the prohibition of affinity (musaharah) is established by it. Thus, if he commits adultery with a woman, she becomes prohibited to his father and his son, and her mother and her daughter become prohibited to him, just as if he had had intercourse with her through doubt or lawfully. If he had intercourse with the mother of his wife or her daughter, his wife would become prohibited to him. Ahmad explicitly stated this in a report from a group. Similar accounts were narrated from Imran ibn Husayn. This was also the view of al-Hasan, Ata, Tawus, Mujahid, al-Sha'bi, al-Nakha'i, al-Thawri, Ishaq, and the People of Reason (Ashab al-Ra'y). It was narrated from Ibn Abbas that unlawful intercourse does not prohibit (1). This was the view of Sa'id ibn al-Musayyib, Yahya ibn Ya'mur, Urwah, al-Zuhri, Malik, al-Shafi'i, Abu Thawr, and Ibn al-Mundhir; based on what was narrated from the Prophet, peace and blessings be upon him, that he said: "The unlawful [act] does not prohibit the lawful" (2). And because it is an act of intercourse through which the woman does not become a matrimonial bed (firash), it does not cause prohibition, like the intercourse of...