Musannaf Ibn Abi Shayba 13:2139

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: I heard Sufyan saying: If a man emancipates his slave, he is released from the pledge (rahn). If he makes him a mudabbar (stipulates his freedom upon the master's death), he is released from the pledge. If it is a slave woman and he has intercourse with her and she produces a child, she is released from the pledge. If the master is wealthy, the pledge-holder pursues the master for the pledge. If he is insolvent, they (the slave/child) strive (work) for the lesser of their value or the pledge. Sufyan said: He (the slave) returns for what he strove for against the master if he becomes wealthy. The umm al-walad (mother of a child) and the mudabbar do not return against their master for anything, because their service is for the master.