Is it permissible to combine a woman and her stepmother [in marriage]?

A man is permitted to combine in marriage a woman and his father's wife. There is no evidence to suggest that this is disliked (makruh). This does not contradict the rule prohibiting combining two women (which states that if one of them were hypothetically male and the other female, then combining them would be forbidden), because the intent of the prohibition is from both sides. Here, the prohibition is from one side only. If the father's wife were hypothetically a man, then he would not be forbidden from marrying this daughter. Some jurists have indicated the permissibility of combining a wife with the husband's mother or daughter, or his female slave.