Sahih Muslim 1428 a
Anas said:
I also saw the wedding feast of Zainab, and he (the Holy Prophet) served bread and meat to the people, and made them eat to their heart's content, and he (the Holy Prophet) sent me to call people, and as he was free (from the ceremony) he stood up and I followed him. Two persons were left and they were busy in talking and did not get out (of the apartment). He (the Holy Prophet) then proceeded towards (the apartments of) his wives. He greeted with as-Salamu 'alaikum to every one of them and said: Members of the household, how are you? They said: Messenger of Allah, we are in good state 'How do you find your family? He would say: In good state. When he was free from (this work of exchanging greetings) he came back, and I also came back along with him. And as he reached the door, (he found) that the two men were still busy in talking. And when they saw him having returned, they stood up and went out; and by Allah! I do not know whether I had informed him, or there was a revelation to him (to the affect) that they had gone. He (the Holy Prophet) then came back and I also returned along with him, and as he put his step on the threshold of his door he hung a curtain between me and him, and (it was on this occasion) that Allah revealed this verse: (" O you who believe), do not enter the houses of the Prophet unless permission is given to 'you" (xxxiii. 53).
قَالَ أَنَسٌ وَشَهِدْتُ وَلِيمَةَ زَيْنَبَ فَأَشْبَعَ النَّاسَ خُبْزًا وَلَحْمًا وَكَانَ يَبْعَثُنِي فَأَدْعُو النَّاسَ فَلَمَّا فَرَغَ قَامَ وَتَبِعْتُهُ فَتَخَلَّفَ رَجُلاَنِ اسْتَأْنَسَ بِهِمَا الْحَدِيثُ لَمْ يَخْرُجَا فَجَعَلَ يَمُرُّ عَلَى نِسَائِهِ فَيُسَلِّمُ عَلَى كُلِّ وَاحِدَةٍ مِنْهُنَّ ‏"‏ سَلاَمٌ عَلَيْكُمْ كَيْفَ أَنْتُمْ يَا أَهْلَ الْبَيْتِ ‏"‏ ‏.‏ فَيَقُولُونَ بِخَيْرٍ يَا رَسُولَ اللَّهِ كَيْفَ وَجَدْتَ أَهْلَكَ فَيَقُولُ ‏"‏ بِخَيْرٍ ‏"‏ ‏.‏ فَلَمَّا فَرَغَ رَجَعَ وَرَجَعْتُ مَعَهُ فَلَمَّا بَلَغَ الْبَابَ إِذَا هُوَ بِالرَّجُلَيْنِ قَدِ اسْتَأْنَسَ بِهِمَا الْحَدِيثُ فَلَمَّا رَأَيَاهُ قَدْ رَجَعَ قَامَا فَخَرَجَا فَوَاللَّهِ مَا أَدْرِي أَنَا أَخْبَرْتُهُ أَمْ أُنْزِلَ عَلَيْهِ الْوَحْىُ بِأَنَّهُمَا قَدْ خَرَجَا فَرَجَعَ وَرَجَعْتُ مَعَهُ فَلَمَّا وَضَعَ رِجْلَهُ فِي أُسْكُفَّةِ الْبَابِ أَرْخَى الْحِجَابَ بَيْنِي وَبَيْنَهُ وَأَنْزَلَ اللَّهُ تَعَالَى هَذِهِ الآيَةَ ‏{‏ لاَ تَدْخُلُوا بُيُوتَ النَّبِيِّ إِلاَّ أَنْ يُؤْذَنَ لَكُمْ‏}‏ الآيَةَ ‏.‏