Narrated Anas bin Malik:

I of all the people know best this verse of Al-Hijab. When Allah's Apostle married Zainab bint Jahsh she was with him in the house and he prepared a meal and invited the people (to it). They sat down (after finishing their meal) and started chatting. So the Prophet went out and then returned several times while they were still sitting and talking. So Allah revealed the Verse: 'O you who believe! Enter not the Prophet's houses until leave is given to you for a meal, (and then) not (so early as) to wait for its preparation .....ask them from behind a screen.' (33.53) So the screen was set up and the people went away.

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، عَنْ أَيُّوبَ، عَنْ أَبِي قِلاَبَةَ، قَالَ أَنَسُ بْنُ مَالِكٍ أَنَا أَعْلَمُ النَّاسِ، بِهَذِهِ الآيَةِ آيَةِ الْحِجَابِ، لَمَّا أُهْدِيَتْ زَيْنَبُ إِلَى رَسُولِ اللَّهِ ﷺ كَانَتْ مَعَهُ فِي الْبَيْتِ، صَنَعَ طَعَامًا، وَدَعَا الْقَوْمَ، فَقَعَدُوا يَتَحَدَّثُونَ، فَجَعَلَ النَّبِيُّ ﷺ يَخْرُجُ، ثُمَّ يَرْجِعُ، وَهُمْ قُعُودٌ يَتَحَدَّثُونَ، فَأَنْزَلَ اللَّهُ تَعَالَى يَا أَيُّهَا الَّذِينَ آمَنُوا لاَ تَدْخُلُوا بُيُوتَ النَّبِيِّ إِلاَّ أَنْ يُؤْذَنَ لَكُمْ إِلَى طَعَامٍ غَيْرَ نَاظِرِينَ إِنَاهُ إِلَى قَوْلِهِ مِنْ وَرَاءِ حِجَابٍ فَضُرِبَ الْحِجَابُ، وَقَامَ الْقَوْمُ.