Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) said that Aishah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), intended to buy a slave girl and set her free, but her owners said: We will sell her, but the wala' will be ours. Aishah (may Allah be pleased with her) mentioned this to the Prophet (peace and blessings be upon him). He (peace and blessings be upon him) said: "Let nothing stop you; the wala' belongs to the one who frees."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الولاء / 21466