Sayyiduna Anas (may Allah be pleased with him) said: When the waiting period ('iddah) of Sayyidah Zaynab (may Allah be pleased with her) was completed, the Prophet (peace and blessings be upon him) said to Zayd (may Allah be pleased with him): "Go to her and mention me to her (as a suitor)." Zayd (may Allah be pleased with him) said: I set out, and when I saw her, I found her leavening her dough. I could not bring myself to look at her because of how great she had become in my heart when I knew that the Prophet (peace and blessings be upon him) had mentioned her. So I said: "The Messenger of Allah (peace and blessings be upon him) has mentioned you." She said: "I will not do anything until I consult my Lord." She stood up and went to her place of prayer, and the Qur'an was revealed, and the Prophet (peace and blessings be upon him) came and entered upon her without permission. Sayyiduna Anas (may Allah be pleased with him) said: We were fed bread and meat at her (wedding feast) until the day was well advanced. The people left, but some men stayed behind in the house talking after the meal. Sayyiduna Anas (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) went out and I followed him. The Messenger of Allah (peace and blessings be upon him) began going round the apartments of his wives and greeting them with salam, and they would say: O Messenger of Allah, how did you find your wife? He said: I do not know whether I told him that the people had left or whether he was told. He went on until he came to the house and entered it. I was about to enter with him, but he let the curtain fall between me and him, and the (command of) hijab was revealed, and the people were admonished with what they were admonished with. (Allah) said: "O you who believe, do not enter the houses of the Prophet unless permission is given to you" [Surah al-Ahzab: 53] until He reached: "Indeed, that would be grave in the sight of Allah" [Surah al-Ahzab: 53].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13360