permissible for anyone to say that the prohibition against marrying them concurrently derives from the Sunnah alone, not the Quran, for Allah says in His Book after listing the women forbidden in marriage:
“Lawful to you are all beyond these, provided that you seek them with your wealth, seeking chastity, not fornication.” [al-Nisā’: 24]
His words, “Do not marry women whom your fathers married, except for what has already occurred” [al-Nisā’: 22], also include paternal grandfathers and their forefathers, whether related by blood or breastfeeding.
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If a man marries a woman and her daughter in a single marriage contract, and this is discovered before he has consummated marriage with either, he must be separated from both without divorce. Neither is entitled to any dowry, and he may marry whichever of them he wishes. It has also been said that he may not marry the mother because of the legal doubt concerning the daughter. If the husband dies, neither woman is entitled to inherit from him, nor must either observe a waiting period.
If, however, this is not discovered until he has consummated marriage with both, he must likewise be separated from them without divorce. Each is entitled to her specified dowry and must observe a waiting period of three menstrual periods to establish that she is not pregnant. Neither may ever lawfully marry him. If he dies, neither is entitled to inherit from him.
If this is discovered after he has consummated marriage with one of them, and her identity is known, he must be separated from her. The woman with whom he consummated marriage is entitled to her specified dowry and must observe a waiting period of three menstrual periods to establish that she is not pregnant. The woman with whom he did not consummate marriage becomes permanently forbidden to him. He may lawfully marry the woman with whom he consummated marriage if she is the daughter, without disagreement; if she is the mother, the matter is disputed. If he dies, neither is entitled to inherit from him in this case either.
If this is discovered after he has consummated marriage with one of them, but it is not known which, and each claims that she is the one with whom he consummated marriage, the husband’s statement, supported by his oath, is accepted in identifying the woman with whom he acknowledges having consummated marriage. He must pay her dowry, and each woman must observe a waiting period of three menstrual periods to establish that she is not pregnant. If he dies, the lesser of the two dowries is taken from his estate and divided between the two wives after both have sworn oaths.
The same ruling applies to a man who marries two sisters in a single contract, except that he may marry whichever of them he wishes after the waiting period of three menstrual periods, if he has consummated marriage with both. Allah alone grants success.
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If, however, he marries the mother and daughter successively, there are six possible cases: