The ruling on one who doubts whether he recited al-Fatihah in the first rak'ah

Question:
A questioner says: Honorable Shaykh, if a person praying doubts that he did not recite al-Fatihah in the first rak'ah, what should he do? And is reciting al-Fatihah obligatory in every rak'ah?

Answer:
In the name of Allah, the Most Gracious, the Most Merciful. Praise be to Allah, Lord of the worlds, and may Allah send prayers and blessings upon our Prophet Muhammad, and upon his family and all his Companions. Reciting al-Fatihah in every rak'ah of the prayers is a pillar of the prayer, and the prayer is not valid without it for the imam and the one praying alone. As for the ma'mum, there is a difference of opinion among the scholars. Some say that the imam's recitation suffices for the ma'mum's recitation, and the ma'mum listens to the imam's recitation. Others say that it is obligatory even for the ma'mum to recite it during the imam's pauses. In any case, if he doubts whether he recited al-Fatihah while he is in the middle of the rak'ah before bowing, he recites al-Fatihah. He recites al-Fatihah to be certain that he has fulfilled this pillar. However, if he does not doubt until after he has bowed or prostrated, then the rak'ah he prayed is void. It is considered invalid, and the second rak'ah takes its place, becoming the first, and he builds upon it. Then, when he completes his prayer, he prostrates for forgetfulness. This is if the doubt occurs during the prayer regarding the recitation of al-Fatihah, and he is the imam or praying alone. But if the doubt does not occur for him until after he has finished the prayer, he does not pay attention to it, because doubt in an act of worship after completing it is not considered. Yes.