Sayyida Amrah bint Abd al-Rahman (may Allah have mercy on her) says that Barirah (may Allah be pleased with her) came to Sayyida Aisha (may Allah be pleased with her) seeking help. Sayyida Aisha (may Allah be pleased with her) said: "If your owners agree, I will pay your price in one lump sum." Barirah (may Allah be pleased with her) went and told them, and they said, "We will not do that, but if your wala' (allegiance) remains with us, then we will do it." Amrah (may Allah have mercy on her) thinks that Sayyida Aisha (may Allah be pleased with her) narrated that the Prophet (peace and blessings be upon him) said to her: "Buy Barirah and set her free, for wala' belongs to the one who sets free."
Hadith Referenceالسنن المأثورة / باب في أكل لحوم الخيل والبغال والحمير / 584
Hadith Takhrijصحیح بخاری، المکاتب باب بیع المکاتب، رقم: 2564، صحیح مسلم، العتق، باب انما الولاء لمن اعتق، رقم: 1504۔