Maliks Muwatta Book 28, Hadith Number 37.
Section : Prohibition against Intercourse with a Slave-Girl who Belonged to One’s Father.
Yahya related to me from Malik from Yahya ibn Said that Abu Nahshal ibn al-Aswad said to al-Qasim ibn Muhammad, “I saw a slave-girl of mine uncovered in the moonlight, and so I sat on her as a man sits on a woman. She said that she was menstruating, so I stood up and have not gone near her after that. Can I give her to my son to have intercourse with?” Al-Qasim forbade that.