Musannaf Ibn Abi Shayba 13:918

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Sufyan, from Hammad, regarding a man who permits his slave to incur debt, then his master emancipates him. He said: His master guarantees the value. Sufyan said: He (the master) pursues his (the slave's) creditors for what remains of the debt.