Musannaf Ibn Abi Shayba 19:173

Abu Bakr narrated to us, he said: Ibn 'Ulayyah narrated to us, from Yunus, from al-Hasan, he said: The *umm al-walad* (a slave woman who has borne a child for her master), the one who falsely accuses her of unchastity is not to be flogged.