Yahya related to me from Malik from Yahya ibn Said that Said ibnal-Musayyab said, "It is forbidden to be married to a woman and herpaternal or maternal aunt at the same time, and for a man to haveintercourse with a female slave who is carrying another man's child."
USC-MSA web (English) reference: Book 28, Hadith 21
Arabic reference: Book 28, Hadith 1115