Busr bin Sa'id (may Allah have mercy on him) narrates from Khawwat bin Jubayr (may Allah be pleased with him) that a man of the Ansar made a will (appointing him); he had an umm walad and a free wife. There was some dispute between the free wife and the umm walad, and the free wife said: "O wretch, you will be sold!" So Khawwat (may Allah be pleased with him) came to the Messenger of Allah (peace and blessings be upon him). The Messenger of Allah (peace and blessings be upon him) said: "She is not to be sold," and he (peace and blessings be upon him) ordered that she be set free.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21778