Musannaf Ibn Abi Shayba 13:1778

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from Yunus, from al-Hasan, that he used to say: If a man emancipates a share of a slave he owns in partnership, he shall guarantee the remainder of him if he is wealthy. And if he is insolvent, the slave shall be made to work to earn his freedom (istus‘a).