Musnad Ahmad 695:16

Al-Walid ibn Muslim narrated to us, Al-Awza’i narrated to us, Al-Zuhri narrated to us, from Al-Tufayl ibn al-Harith—and he was a man from Azd Shanu'ah, and he was a brother to Aisha through her mother, Umm Ruman—and he mentioned the hadith. He sought the help of Al-Miswar ibn Makhramah and Abd al-Rahman ibn al-Aswad ibn Abd Yaghuth regarding her. They asked her for permission, and she granted them permission. They spoke to her and adjured her by Allah and by kinship, and by the saying of the Messenger of Allah (may Allah bless him and grant him peace): "It is not lawful for a Muslim man to forsake his brother for more than three [days]."