Sayyiduna Anas (may Allah be pleased with him) said: Sayyidah Zaynab bint Jahsh (may Allah be pleased with her) used to boast over the other wives, saying that Allah Almighty had arranged her marriage in the heavens, and the verse of hijab was revealed concerning her. The narrator said: People were sitting in the house of the Prophet (peace and blessings be upon him); he went out, then came back, then went out again, and the people were still sitting. Signs of displeasure were seen on his (peace and blessings be upon him) face, and (because of this) the verse of hijab was revealed: "O you who believe, do not enter the houses of the Prophet unless permission is given to you" [Surah al-Ahzab: 53].
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13362