Musannaf Ibn Abi Shayba 3:2979

Abu Bakr narrated to us, he said: Waki’ narrated to us, from Shu’bah, he said: I asked al-Hakam and Hammad about the man who comes on the day of Jumu’ah before the Imam gives the taslim. They both said: He should pray two rak’ahs.