The ruling on one who adds a rak'ah to his prayer while doubting that he did not add

May Allah forgive you, O Shaykh! A man stood to pray at night, and he prayed three rak'ahs while he thought he had prayed two, then after another person informed him that he had prayed three, he said: I prayed two rak'ahs,And after he was certain, he said: my intention was not for three rak'ahs, but my intention was to pray two rak'ahs. Then he stood and made this rak'ah even (paired), then he continued with the witr, then he performed the witr at the end of the night. What is the ruling on this?
This is not correct.We say: If he is reminded that he prayed three, he only prostrates for forgetfulness, since he did not decrease but rather increased. This is unlike the case where he prays three while four are obligatory upon him, such as the Zuhr prayer, and then he is reminded; in that case, he completes it. As for this case, it is better that he not complete it, but rather prostrate for forgetfulness, and that is sufficient.