Yahya related to me from Malik from Yahya ibn Said that AbuNahshal ibn al-Aswad said to al-Qasim ibn Muhammad,"I saw a slave-girlof mine uncovered in the moonlight, and so I sat on her as a man sitson a woman. She said that she was menstruating, so I stood up and havenot gone near her after that. Can I give her to my son to haveintercourse with?" Al-Qasim forbade that.
USC-MSA web (English) reference: Book 28, Hadith 37
Arabic reference: Book 28, Hadith 1132