Musannaf Ibn Abi Shayba 13:2652

Abu Bakr narrated to us, he said: Hushaym narrated to us, from Mughira, from Ibrahim, who said: The children of the *mukātabah* (a female slave who has a contract of manumission) are in her status; they are freed by her freedom and they are enslaved by her enslavement. If she dies, he (the child) strives to pay what remains of her *mukātabah* contract. If they pay it, they are freed, and if they are unable, they are returned (to slavery).