Sunan an-Nasa'i 3450

It was narrated from 'Aishah that she wanted to buy Barirah, but her masters stipulated that her Wala' should go to them. She mentioned that to the Prophet and he said:"Buy her and set her free, for Al-Wala' is to the one who sets the slave free." Some meat was brought and it was said: "This is some of that which was given in charity to Barirah." He said: "It is charity for her and a gift for us." And the Messenger of Allah gave her the choice, and her husband was a free man