Abd al-Rahman bin al-Qasim narrates from his father, and he from Sayyidah Aishah (may Allah be pleased with her), that Sayyidah Aishah (may Allah be pleased with her) bought Barirah from some people of the Ansar, and they stipulated the wala' (for themselves). The Messenger of Allah (peace and blessings be upon him) said: "The wala' belongs to the one who bestowed the favour (of freedom)." Sayyidah Aishah (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) gave Barirah the choice, and her husband was a slave.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13768