Musannaf Ibn Abi Shayba 3:3650

Waki’ narrated to us, from Sufyan, from Maysarah, from al-Minhal ibn ‘Amr, from ‘Abbad ibn ‘Abd Allah, from ‘Ali, who said: The Imam should not perform voluntary prayer in the place where he led the people in prayer until he moves or separates [from that spot] by speaking.