Musannaf Ibn Abi Shayba 13:654

Abu Bakr narrated to us, he said: Abd al-Salam ibn Harb narrated to us, from Mughira, from Ibrahim, regarding a man who marries his slave woman (umm al-walad) to his slave, and she bears children for him. He said: They are in the position of their mother; they are emancipated by her emancipation, and they are enslaved by her enslavement. If their master dies, they are emancipated.