Amrah bint Abd al-Rahman (may Allah have mercy on her) says that Barirah (may Allah be pleased with her) came to Sayyidah Aishah (may Allah be pleased with her) to seek her help. Sayyidah Aishah (may Allah be pleased with her) said: If your people agree, I will pay the whole price at once and free you. So Barirah (may Allah be pleased with her) spoke to her people. They said: If the wala' is ours, then it is fine. Yahya says: Amrah bint Abd al-Rahman stated that Sayyidah Aishah (may Allah be pleased with her) mentioned this to the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) said: "Let nothing stand in your way; buy her and free her, for the wala' belongs to the one who frees."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21722