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.
Sahih al-Bukhari, Vol. 6, Book of Prophetic Commentary on the Qur'an, Hadith 315
Sahih al-Bukhari, Book of Prophetic Commentary on the Qur'an, Hadith 315