Sayyidah Umm Hani bint Abi Talib (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) proposed marriage to me, and I offered him my excuse, and he (peace and blessings be upon him) accepted my excuse. Then Allah revealed this verse: "Indeed, We have made lawful for you your wives" [Al-Ahzab: 50], up to His words: "and the daughters of your maternal aunts who emigrated with you" [Al-Ahzab: 50]. So I was not lawful for him (peace and blessings be upon him), because I had not emigrated with him; I was one of the Tulaqa' (those set free at the Conquest).
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21375