Musannaf Ibn Abi Shayba 19:668

Abu Bakr narrated to us, he said: Ali narrated to us, from Ali ibn Mubarak, from Yahya ibn Abi Kathir, from Ikrimah and Sulayman ibn Yasar, regarding a man who marries a slave woman and had not married a free woman before her, then commits adultery. Sulayman ibn Yasar said: He is to be stoned. And Ikrimah said: He is to be flogged.