What is the wisdom behind restricting marriage to four wives, while there is no restriction on the number of concubines, knowing that both can bear children who are attributed to the father?

Scholars have differed regarding the wisdom behind restricting wives to four. Some believe that the number four achieves companionship and intimacy, which would be lost with an increase, and it also ensures each wife her right to stay overnight after three nights.

Others hold that four wives is a middle ground between the law of Moses, which does not limit the number, and the law of Jesus, which restricts it to one. The wisdom behind this number is that most matters in Islamic law are based on trilogies.

As for the absence of restriction in possessing female slaves (milk al-yamin), it is because a female slave's ownership is not limited to concubinage (sexual intimacy), but also includes service and other benefits. The master can also marry her off to someone else, whereas in a marriage contract (nikah), sexual intimacy is primarily intended.