Musnad Ahmad 1153:1348

Jarir narrated to us, from Mansur, from Ibrahim, from al-Aswad, from Aisha, who said: I purchased Barirah, and her people stipulated her patronage (wala'). I mentioned that to the Messenger of Allah, peace and blessings of Allah be upon him. The Messenger of Allah, peace and blessings of Allah be upon him, said: "Purchase her and emancipate her, for the patronage belongs only to the one who gives the silver." She said: So I purchased her and emancipated her. She said: Then the Messenger of Allah, peace and blessings of Allah be upon him, called her and gave her the choice regarding her husband, and she chose herself, and her husband was a free man.