Musannaf Ibn Abi Shayba 3:2940

Waki’ narrated to us, from Shu’bah, who said: I asked al-Hakam and Hammad about speaking when the Imam has gone out [to the pulpit] until he speaks, and when he descends before he prays. Al-Hakam disliked it, and Hammad said: "There is no harm in it."