Musannaf Ibn Abi Shayba 19:179

Abu Bakr narrated to us, he said: Isma'il ibn Ibrahim narrated to us, from Ayyub, from Nafi', from some of the commanders of the fitnah (civil strife) who asked Ibn 'Umar about an umm walad (a slave woman who has borne a child to her master) who was accused of unchastity. He ordered that the one who accused her be flogged eighty lashes.