Musnad Ahmad 1153:1546

'Abd al-Rahman narrated to us, from Sufyan, from Mansur, from Ibrahim, from al-Aswad, from 'Aishah, that she bought Barirah. She said: I said, "O Messenger of Allah, shall I buy Barirah and stipulate the right of inheritance (al-wala') for them?" He said: "Buy her, for the right of inheritance belongs only to the one who bestowed the favor, or to the one who emancipated."