Musannaf Ibn Abi Shaybah

Hasan (may Allah have mercy on him) says that if a person marries a slave woman and a free woman in a single contract, separation will be enforced between the man and the slave woman. Similarly, if someone marries two sisters in a single contract, separation will be enforced between them.

Ibrahim (may Allah have mercy on him) said that if, in one contract, a man marries both a free woman and a slave woman, then their marriage will be invalid.