Musannaf Ibn Abi Shayba 9:1358

Abu Bakr narrated to us, he said: Ibn Numayr narrated to us, from Sayf, from Ibn Abi Najih, from Mujahid, that he disliked for a man to marry the wife of his mother. He said: And Tawus and 'Ata' did not see any harm in it.