Section Four: If he has had intercourse with one of them, he may not have intercourse with the other before the first one he had intercourse with is prohibited to him, whether by removing her from his possession or by marriage. This is the opinion of Ali, Ibn Umar, al-Hasan, al-Awza'i, Ishaq, and al-Shafi'i. If he pledges her as collateral (rahn), her sister does not become permissible for him, because his prevention from having intercourse with her is due to the right of the pledgee (murtahin), not because she is prohibited; therefore, he may have intercourse with her with the permission of the pledgee, and because he is able to redeem her whenever he wishes and have her return to him. Qatada said: "If he observes the waiting period (istibra') for her, her sister becomes permissible for him," because his bed (firaash) with her has ceased to exist. Thus, if she were to give birth and he denied paternity by claiming the waiting period was completed, it would be disavowed, so it is similar to the case of when he gives her in marriage. Our argument is the statement of Ali and Ibn Umar, and because his ownership of her has not ceased, nor has her permissibility for him, so it is similar to the case of when she is had intercourse with through doubt (shubha) and he observes the waiting period for that intercourse. Moreover, because that does not prevent him from having intercourse with her, he cannot be certain that he will not return to her, making it a pretext for combining them. If he prohibits one of them to himself, the other is not permitted, because this does not make her forbidden; rather, it is an oath that requires expiation. Even if it were to make her forbidden, it is due to an impediment (arid), which he can remove whenever he wishes by expiation, so it is like menstruation, postpartum bleeding, ihram, and fasting. If he enters into a contract of manumission (kitaba) with one of them, the manifest meaning of the words of al-Khiraqi is that the other is not permitted to him. The companions of al-Shafi'i said: "The other is permitted to him," because she has been prohibited to him for a reason he cannot rescind, so it is like marriage. Our argument is that he is in a position to make her permissible in a way that does not depend on others, so her sister is not permitted to him, like the pledged slave girl.

Section Five: If he removes her from his possession, her sister does not become permissible for him until he observes the waiting period (istibra') for the one removed and knows her freedom from pregnancy. Whenever she is pregnant by him, her sister does not become permissible for him until she delivers her child, because he would be combining his fluid in the wombs of two sisters, in the same position as marrying a sister during the waiting period of her sister.

Section: If he has intercourse with his two slave girls who are sisters together, the intercourse with the second is prohibited, and there is no hadd (prescribed punishment) for it, because his intercourse...