Musannaf Ibn Abi Shayba 13:1525

Abu Bakr narrated to us, he said: Yazid bin Harun narrated to us, from Hammad bin Salamah, regarding the *umm al-walad* (a slave woman who has borne a child to her master): If she delivers him while he is a *mudghah* (a lump of flesh), then she has been emancipated by him.