Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: Sayyidah Aishah (may Allah be pleased with her) bought Barirah (may Allah be pleased with her) from the Ansar in order to set her free, and they stipulated that her wala' (right of inheritance through clientage) would remain with them. Sayyidah Aishah (may Allah be pleased with her) accepted this condition. Then when the Prophet (peace and blessings be upon him) came, she informed him of this. He (peace and blessings be upon him) said: "Wala' belongs only to the one who sets free." Then he (peace and blessings be upon him) ascended the pulpit and said: "What is wrong with people that they stipulate conditions that are not in the Book of Allah? Any condition that is not in the Book of Allah is void; it is to be referred back to the Book of Allah." Barirah had a husband, so the Messenger of Allah (peace and blessings be upon him) gave her the choice: if she wished, she could remain with her husband as she was, and if she wished, she could separate from him. So she separated from her husband. Then the Prophet (peace and blessings be upon him) came in and saw a leg of mutton. He (peace and blessings be upon him) said to Aishah (may Allah be pleased with her): "Will you not cook this meat for us?" She said: "This was given in charity to Barirah, and she gave it to us as a gift." He (peace and blessings be upon him) said: "Cook it; it is charity for her and a gift for us."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11694