Musannaf Ibn Abi Shayba 35:142

Al-Fadl ibn Dukayn narrated to us, from Sufyan, from Abu Qays, from Hudhayl, from Abdullah, who said: The Prophet, may Allah bless him and grant him peace, cursed the one who marries a divorced woman to make her lawful for her former husband (al-muhallil) and the one for whom she is made lawful (al-muhallal lahu).