Musannaf Ibn Abi Shayba 13:518

Abu Bakr narrated to us, he said: Abu Khalid al-Ahmar narrated to us, from Yahya ibn Sa'id, from Abu Bakr ibn 'Amr ibn Hazm, that a woman from [the tribe of] Muharib gifted the *wala'* (patronage rights) of her slave to himself, and she emancipated him, and he emancipated himself. He said: So he gifted himself to 'Abd al-Rahman ibn 'Amr ibn Hazm. He said: Then she died, and the *mawla* (the freed slave) disputed [the matter] before 'Uthman ibn 'Affan. 'Uthman called for evidence regarding what he said, so he brought him the evidence. 'Uthman said to him: "Go, and form a *wala'* alliance with whomever you wish." So he formed a *wala'* alliance with 'Abd al-Rahman ibn 'Amr ibn Hazm.