Malik related to me from Yahya ibn Said from Amra bint Abd ar-
Rahman that Barira came asking the help of A'isha, umm al-muminin.
A'isha said, "If your masters agree that I pay them your price in one
lump sum and set you free I will do it." Barira mentioned that to her
masters and they said, "No, not unless your wala' is ours." Yahya ibn
Said added that Amra bint Abd ar-Rahman claimed that A'isha mentioned
that to the Messenger of Allah, may Allah bless him and grant him
peace, and the Messenger of Allah, may Allah bless him and grant him
peace said, "Buy her and set her free. The wala' only belongs to the
one who sets free."
Muwatta Malik Book 38, Hadith 20