Musannaf Ibn Abi Shayba 13:917

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, from Ibrahim, that he used to say regarding the slave who has been granted permission to trade: If he has a debt upon him and his master emancipates him, the slave shall work to pay off their debt. Emancipation does not increase him except in goodness.