The World Federation One Stop Fiqh

Ruling 1161

If a person doubts whether or not he performed an act that is not a rukn of the prayer, in the event that he has not started to perform the act after it, he must perform it. For example, if before reciting the other surah he doubts whether or not he recited Sūrat al-Ḥamd, he must recite Sūrat al-Ḥamd. If after performing it he remembers that he had recited it, his prayer is valid as he will not have performed an additional rukn.