Аль-Ахзаб 33:37

Zayd’s marriage with Zaynab took place in the year 4 AH, but the marriage was a failure and the next year they separated. When Zayd expressed to the Prophet, his intention of giving a divorce in this case, the Prophet of God asked the reason for it. Zayd said that she had a superiority complex over him due to her being from a noble family. However, the Prophet Muhammad urged him not to divorce her. However, on Zayd’s insistence, he permitted them to separate. When Zayd and Zaynab got married, they broke an old convention and it was ordained that a difference in social status should not come in the way of marriage. But when they separated, it was the will of Almighty God that Zaynab should be made the means of breaking yet another erroneous custom. By tradition, in the old pre-Islamic period, an adopted son was treated just like a real son, enjoying the same rights and titles. The best way of breaking this custom was that after her divorce, Zaynab should marry the Prophet Muhammad. Zayd was the adopted son of the Prophet Muhammad, and was known as Zayd bin (son of) Muhammad. Under these circumstances, the Prophet’s marrying the divorced wife of his adopted son amounted to a disastrous contravention of the old custom, which held that a man’s marrying a woman formerly married to his adopted son, and then divorced by him, was prohibited because she was no different from a woman married to and then divorced by his real son. The Prophet Muhammad was told in advance that if there should be a separation between the aforesaid couple, then as a device to break the old pre-Islamic custom, Zaynab would be given in marriage to him. Since such a marriage in the prevailing atmosphere would have given him a bad name, the Prophet urged Zayd not to divorce Zaynab, so that he might be spared this very trying ordeal. But, whatever was ordained by God, did happen. Zayd divorced Zaynab and, so as to break the old custom, Zaynab was married to the Prophet in the year 5 A.H.