What should two worshippers do if one of them suspects a raka'ah is missing while the other is certain it is complete, and does the ruling differ if each of them is certain of something different?

Doubt concerning the number of rak'ahs after completing the prayer is to be disregarded. The questioner and his companion should turn away from these whispers (waswas). As long as you are certain that you have completed the prayer, do not pay attention to what the ma'mum (follower) says, even if he gestures or informs you before the taslim (salutation), unless the number of informers is very large. A ma'mum who is frequently doubtful, his doubts are not to be heeded. If he is not frequently doubtful, and he becomes certain of his imam's completion of the prayer before its end, then it is not permissible for him to continue following him. It is preferable to achieve congregational prayer in the mosque if possible.