Musannaf Ibn Abi Shayba 13:1808

Abu Bakr narrated to us, he said: Husayn bin Ali narrated to us, from Za'idah, from Mansur, who said: Ibrahim said regarding a man who emancipated a slave of his at the time of his death, and he had no wealth other than him: Ibrahim said: One-third of him is emancipated, and he strives [to earn his freedom] for the remaining two-thirds.