Musannaf Ibn Abi Shayba 13:1812

Abu Bakr narrated to us, he said: Yazid ibn Harun narrated to us, from Hammad ibn Salamah, from Hammad, from Ibrahim, who said: If one emancipates a portion of his slave during his terminal illness, the whole of him is emancipated. If it exceeds one-third, he (the slave) works to earn the remainder of the one-third.