Musannaf Ibn Abi Shayba 19:177

Abu Bakr narrated to us, he said: Abd al-A’la narrated to us, from Ma’mar, from al-Zuhri, he said: The one who falsely accuses an *umm al-walad* (a slave woman who has borne a child to her master) is not to be flogged with the prescribed punishment (*hadd*).