Musannaf Ibn Abi Shayba 3:5733

Ghundar narrated to us, from Shu'bah, who said: I asked al-Hakam and Hammad about a man who speaks during the prayer. They said: If he speaks when he has finished his prayer and added [something], then it has passed, and upon him are the two prostrations of forgetfulness. And if he speaks while he has not completed his prayer, then he must repeat it.