Muwatta Malik 1112

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّهُ كَانَ يَقُولُ يُنْهَى أَنْ تُنْكَحَ الْمَرْأَةُ عَلَى عَمَّتِهَا أَوْ عَلَى خَالَتِهَا وَأَنْ يَطَأَ الرَّجُلُ وَلِيدَةً وَفِي بَطْنِهَا جَنِينٌ لِغَيْرِهِ ‏.‏

Yahya related to me from Malik from Yahya ibn Said that Said ibn al-Musayyab said, "It is forbidden to be married to a woman and her paternal or maternal aunt at the same time, and for a man to have intercourse with a female slave who is carrying another man's child

Reference

Muwatta Malik 1112

In-book

Book 28, Hadith 22