Musannaf Ibn Abi Shayba 35:239

Abu Mu'awiyah narrated to us, from al-A'mash, from Ibrahim, from al-Aswad, from 'Aishah, who said: The family of Barirah wanted to sell her and stipulate the right of inheritance (al-wala'). She mentioned that to the Prophet, peace and blessings of Allah be upon him. He said: "Buy her and emancipate her, for the right of inheritance (al-wala') belongs to the one who emancipates."