Musnad Ahmad 1153:1013

Ja'far ibn 'Awn narrated to us, Yahya ibn Sa'id narrated to us, from 'Amrah, from 'Aishah, who said: Barirah came to me seeking my assistance regarding her *kitabah* (contract of manumission). I said to her: "If your masters wish, I will pay them your price in one lump sum and set you free." She sought the permission of her masters, and they said: "No, unless you stipulate the *wala'* (right of inheritance) for us." The Messenger of Allah, peace and blessings of Allah be upon him, said: "Buy her, for the *wala'* belongs to the one who sets free."