Anas bin Malik (may Allah be pleased with him) said: I am the most knowledgeable of people about this verse. When Zaynab (may Allah be pleased with her) was brought as a bride to the Messenger of Allah (peace and blessings be upon him), she was with him (peace and blessings be upon him) in the house, and he (peace and blessings be upon him) prepared food. The people came, and the Messenger of Allah (peace and blessings be upon him) would go out while the people stayed in their places, and he would come back while the people were still sitting. So Allah revealed: "O you who believe! Do not enter the houses of the Prophet unless permission is given to you for a meal, without waiting for it to be cooked; but when you are invited, then enter, and when you have eaten, disperse, and do not linger for conversation. Indeed, that troubles the Prophet, and he is shy of you, but Allah is not shy of the truth. And when you ask his wives for anything, ask them from behind a screen" [al-Ahzab: 53]. So the Messenger of Allah (peace and blessings be upon him) let down the screen and the people stood up.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20499