Sunan An-Nasa'i

It was narrated that 'Aishah said:""I bought Barirah and her masters stipulated that her loyalty (Wala) should be to them, I mentioned that to the Prophet and he said: 'Set her free, and loyalty belongs to the one who pays the silver.''' She said: ""so I set her free. The Messenger of Allah called her and gave her the choice regarding her husband, and she chose herself. Her husband was a free man