Musnad Ahmad 1153:501

Ishaq ibn Isa narrated to us, he said: Muslim narrated to me, from Hisham ibn Urwah, from his father, from Aisha, that a man bought a slave, and he utilized his earnings. Then he found—or saw—a defect in him, so he returned him due to the defect. The seller said: "[I want] the earnings of my slave." The Prophet, peace and blessings of Allah be upon him, said: "The earnings are in return for the liability."