Musannaf Ibn Abi Shayba 9:1174

Marwan ibn Mu'awiyah narrated to us, from al-Ala' ibn al-Musayyab, from his father, who said: Umar said: "If a man were brought to me who had engaged in mut'ah (temporary marriage) with a woman, I would stone him if he were previously married (muhsan). And if he were not previously married, I would flog him."