Musannaf Ibn Abi Shayba 13:1552

Abu Bakr narrated to us, he said: Abu al-Ahwas narrated to us, from Simak, from Qabus ibn Abi al-Mukhariq, from his father, who said: Ali sent Muhammad ibn Abi Bakr to Egypt. He wrote to him asking him about a *mukātab* (a slave who has a contract of manumission) who died and left behind wealth and children. He wrote, ordering in the letter: If he left behind enough to fulfill his *kitābah* (contract of manumission), his masters are to be summoned and they shall take their due in full. Whatever remained was an inheritance for his children.