Translation:

37. Behold! thou didst say to one who had received the grace of Allah and thy favor: "Retain thou (in wedlock) thy wife and fear Allah." But thou didst hide in thy heart that which Allah was about to make manifest: thou didst fear the people but it is more fitting that thou shouldst fear Allah. Then when Zaid had dissolved (his marriage) with her with the necessary (formality) We joined her in marriage to thee: in order that (in future) there may be no difficulty to the Believers in (the matter of) marriage with the wives of their adopted sons when the latter have dissolved with the necessary (formality) (their marriage) with them: and Allah's command must be fulfilled.

Notes (Tafseer)

3722. This was Zaid son of Haritha, one of the first to accept the faith of Islam. He was a freedman of the holy Prophet, who loved him as a son and gave him in marriage his own cousin Zainab. The marriage however turned out to be unhappy. See next note.

3723. Zaid's marriage with the Prophet's cousin Zainab daughter of Jahsh did not turn out happy. Zainab the high-born looked down upon Zaid the freedman who had been a slave. And he was not comely to look at. Both were good people in their own way, and both loved the Prophet, but there was mutual incompatibility and this is fatal to married life. Zaid wished to divorce her, but the Prophet asked him to hold his hand, and he obeyed. She was closely related to the Prophet; he had given a handsome marriage gift on her marriage to Zaid; and people would certainly talk if such a marriage was broken off. But marriages are made on earth, not in heaven, and it is no part of Allah's Plan to torture people in a bond which should be a source of happiness but actually is a source of misery. Zaid's wish-indeed the mutual wish of the couple-was for the time being put away, but it became eventually an established fact, and everybody came to know of it.

3724. All actual facts are referred to Allah. When the marriage is unhappy, Islam permits the bond to be dissolved, provided that all interests concerned are safeguarded. Apparently there was no issue here to be considered. Zainab had to be considered, and she obtained the dearest wish of her heart in being raised to be a Mother of the Believers, with all the dignity and responsibility of that position. See n. 3706 to xxxiii. 28 above.

3725. The Iddat or period of waiting after divorce (ii. 228, and n. 254) was duly completed.

3726. The Pagan superstition and taboo about adopted sons had to be destroyed. See xxxiii. 4-5 and notes 3671-3672 above.