Musannaf Ibn Abi Shayba 13:2859

Abu Bakr narrated to us, he said: Ubaydullah narrated to us, from Ibrahim ibn Isma'il, from Taliq ibn 'Imran, from Abu Burdah, from Abu Musa, that the Prophet, peace and blessings of Allah be upon him, forbade that a mother and her child be separated in a sale.