Sahih Muslim Book 8, Hadith Number 3330.

Chapter: Pertaining to the marriage of Zainab bint Jahsh with the Holy Prophet (May peace be upon him) and verses pertaining to purdah veil).

Anas (Allah be pleased with him) reported: When the ‘Iddah of Zainab was over, Allah’s Messenger (May peace be upon him) said to Zaid to make a mention to her about him. Zaid went on until he came to her and she was fermenting her flour. He (Zaid) said: As I saw her I felt in my heart an idea of her greatness so much so that I could not see towards her (simply for the fact) that Allah’s Messenger (May peace be upon him) had made a mention of her. So I turned my back towards her and I turned upon my heels, and said: Zainab, Allah’s Messenger (May peace be upon him) has sent (me) with a message to you. She said: I do not do anything until I solicit the will of my Lord. So she stood at her place of worship and the (verse of) the Qur’an (pertaining to her marriage) were revealed, and Allah’s Messenger (May peace be upon him) came to her without permission. He (the narrator) said: I saw that Allah’s Messenger (May peace be upon him) served us bread and meat until it was broad day light and the people went away, but some persons who were busy in conversation stayed on in the house after the meal. Allah’s Messenger (May peace be upon him) also went out and I also followed him, and he began to visit the apartments of his wives greeting them (with the words): As-Salamu ‘alaikum, and they would say: Allah’s Messenger, how did you find your family (Hadrat Zainab)? He (the narrator) stated: I do not know whether I had informed him that the people had gone out or he (the Holy Prophet) informed me (about that). He moved on until he entered the apartment, and I also went and wanted to enter (the apartment) along with him, but he threw a curtain between me and him, as (the verses pertaining to seclusion) had been revealed, and people were instructed in what they had been instructed. Ibn Rafii had made this addition in his narration: “O you who believe, enter not the houses of the Prophet unless permission is given to you for a meal, not waiting for its cooking being finished…” to the words “…Allah forbears not from the truth.”