All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
When one is doubtful whether or not he recited Al-Faatihah in the prayer it involves some relevant detailing. When the doubt occurs in the same Rak‘ah, one has to recite Al-Faatihah and then perform the actions that follow it. If the doubt occurs in the same prayer but in a different Rak‘ah, then one has to nullify the doubtful Rak‘ah and add another one at the end of the prayer. Doubts that occur after the prayer are harmless since they have no effect once an act of worship is over. This is the ruling when the doubt is natural. However, when doubt is often and dominant, the scholars of Fiqh state that it is ineffective and should be ignored.