Musannaf Ibn Abi Shayba 19:185

Abu Bakr narrated to us, he said: Abda narrated to us, from Sa’id, from Abu Ma’shar, from Ibrahim, regarding the *umm al-walad* (a slave woman who has borne a child for her master): If she is emancipated and then she is accused of unchastity, the one who accused her is to be flogged.