as many concubines as a man wishes, without any numerical limit, because slave women are not entitled to an equitable division of his time, nor do they have a right to intercourse with him. Thus, he may own a woman with whom intercourse is unlawful for him, such as his wife’s mother or daughter, or his sister or daughter through breastfeeding. Even if he were impotent or had sworn to abstain from intercourse, he would not be required to relinquish ownership of her. With wives, however, he must divide his time equitably among them.

“The best company consists of four.”

The equitable treatment that most people can manage therefore extends to four. As for the Messenger of Allah, may Allah bless him and grant him peace, Allah empowered him to deal justly with more than that—according to the well-known view that he was obliged to divide his time equitably. According to the other view, he was exempt from this obligation. Likewise, because he had a greater claim upon the believers than they had upon themselves, he was permitted to marry without a dowry.

They said:

Since the “prohibition on exceeding the permitted number of wives” rests solely on the obligation to divide one’s time equitably, and this consideration does not apply to slave women, he is not forbidden to take more than four concubines. This differs from taking two sisters together: that prohibition serves to prevent the severing of kinship ties between them, a consideration that applies to two slave women just as it does to two wives. If he takes both sisters as concubines, the same jealousy will arise between them as would arise if he married them both, leading to the severing of kinship ties.

Since this consideration is the operative basis of the ruling in Islamic law, he may marry two women together if they have a relationship that bars intermarriage but no blood ties, or blood ties that do not bar intermarriage. An example of the first is marrying both a woman and her husband’s daughter. Thus, after the death of ʿAlī ibn Abī Tālib, ʿAbd Allāh ibn Jaʿfar was married to both ʿAlī’s widow and his daughter.