Musannaf Ibn Abi Shayba 7:125

Ibn Numayr narrated to us, from Abu Hanifa, from Hammad, from Ibrahim, who said: "The child of his *mukātab* (a slave who has a contract of manumission) does not suffice in [expiation for] *ẓihār*, nor in the freeing of a slave, nor in [expiation for] killing."