All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It was authentically narrated on the authority of Masrooq that ‘Aa'ishah said, “Were the Prophet to conceal anything of the Quran, he would have concealed this verse: {And (remember, O Muhammad) when you said to the one on whom Allah bestowed favor and you bestowed favor, ‘Keep your wife and fear Allah,’ while you concealed within yourself that which Allah is to disclose...} [Quran 33:37] [At-Tirmithi 3/353; Hasan-Saheeh (good or sound)]
As for the reason for the revelation of this verse, Ibn Al-‘Arabi chose the following as the preponderant reason:
“When Zayd married Zaynab, Jibreel (Gabriel) came to the Prophet, sallallaahu ‘alayhi wa sallam, and said, ‘Zaynab has been made your wife!’ Soon after, Zayd came (to the Prophet, sallallaahu ‘alayhi wa sallam) asking to end his marriage with Zaynab. The Prophet, sallallaahu ‘alayhi wa sallam, said to him, ‘Fear Allah and keep your wife!’ However, Zayd insisted on divorcing her. He divorced her, and when her waiting period was over, the Messenger of Allah, sallallaahu 'alayi wa sallam, proposed to her through his freed slave, Zayd (her ex-husband), and Allah revealed the verse that mentioned this incident. The verse means: And remember, O Muhammad, when you said to the one on whom Allah bestowed favor and on whom you bestowed favor: Keep your wife and fear Allah in divorcing her, and you concealed in your heart what Allah would disclose; i.e. your decreed marriage to her. The Prophet, sallallaahu ‘alayhi wa sallam, knew with certainty that since it was revealed to him that she was his wife, then this would inevitably happen and become known, because what Allah reveals must happen exactly as He revealed it.” [Ahkaam Al-Quran, 3/578]
For more benefit, please refer to fatwas 177139 and 139996.
Allah knows best.