Musannaf Ibn Abi Shaybah

Hazrat Mujahid (may Allah have mercy on him) considered it disliked for a man to marry the wife of his mother's husband, while Hazrat Tawus (may Allah have mercy on him) and Ata (may Allah have mercy on him) did not see any harm in it.

Hazrat Aamir (may Allah have mercy on him) says that there is no harm if a man marries the wife of his mother's husband.

Hazrat Ibn Abbas (may Allah be pleased with them both) says: Do not form a bond with one with whom either of your parents has formed a bond, such as your mother's husband.