Nasai

1330. Commentary: When the imam believes that he has completed the prayer and has finished it, in this state, if he engages in any speech, or in the case of being a follower (muqtadi), he alerts the imam and is required to speak, or if, for the purpose of verification, there is mutual conversation, then after realizing (the mistake), the greeting (salam) and speech will not invalidate the prayer. If the remainder of the prayer is performed and the prostrations of forgetfulness (sujud as-sahw) are made, then the prayer is undoubtedly valid. This is clearly understood from the ahadith. However, the Hanafis and Hanbalis hold the view that in the case of speech, the prayer must be performed anew. But their position is not supported by the ahadith. (For further details, see Hadith: 1225, 1230)