The ruling on one who doubts the number of rak'ahs during the prayer

Question:
May Allah reward you, Honorable Shaykh. This questioner says: I am the imam of a mosque, and sometimes I doubt during the prayer, so I do not know if I am in the third or fourth rak'ah, and nothing is more likely in my mind, so I say to myself, I will sit assuming it is the fourth, but it was not, for the ma'mum (those praying behind the imam) will alert me to that. This happens to me in some periods, and then I do not perform the prostration for forgetfulness. The question is: what is obligatory for me regarding the prostration for forgetfulness in this state? And is there a sin on me if I leave it?

Answer:
If you doubt in the prayer, then you build upon certainty. So if you doubt whether you prayed three or four, then you make it three and you come with the fourth and you sit, this is what is obligatory for you. And if you doubt, then when the doubt is removed and you know your state, if you completed the prayer, then you prostrate for the doubt that occurred in your prayer; you prostrate for this hesitation because part of the prayer passed while you were in doubt, so you prostrate for the doubt.