Malik related to me from Nafi from Abdullah ibn Umar that Umaribn al-Khattab said, "If a slave-girl gives birth to a child by hermaster, he must not sell her, give her away, or bequeath her. Heenjoys her and when he dies she is free ."
USC-MSA web (English) reference: Book 38, Hadith 6
Arabic reference: Book 38, Hadith 1471