Musannaf Ibn Abi Shaybah 8327 — Speaking in prayer

Shu'bah said: I asked al-Hakam and Hammad what the ruling is if a man speaks during the prayer. They said: If he spoke after he had completed the prayer, while adding something extra, then his prayer is valid and he should perform the prostrations of forgetfulness; and if he spoke before completing the prayer, he must pray it again.