If the One Who is led in Prayer is in Doubt over whether He has recited the Tahiyyat or not
Question :
If the Imam makes the Taslim and I am in doubt over whether I have recited the Tahiyyat or not, what should I do in this situation?
Answer:
No attention should be paid to doubt occurring after the completion of an act of worship. Rather you should maintain your original view, for it is most usual for a person to perform the obligatory acts and the pillars of prayer to the best of his knowledge. But if he is taken by doubt during the prayer, he should base his assumption on that which he is sure of, and in this way, he will safeguard his acts of worship. He should pay no attention to doubts that afflict him after he has finished the prayer.
Source:
Ibn Jibreen
Fatawa Islamiyah, Vol. 2 Page 272