If one repeats the Basmala at the beginning of Al-Fatiha after doubting its validity, is this considered interrupting a pillar in order to return to a Sunnah, and does it necessitate repeating the prayer?

The prayer of one who doubts reciting the Basmalah after starting Al-Fatihah is not invalidated if he interrupts Al-Fatihah, recites the Basmalah, and then repeats Al-Fatihah. This is because the Basmalah is considered part of Al-Fatihah by some jurists. Whoever omits it or doubts it is obligated to recite it to resolve the difference of opinion. As for those who consider the Basmalah a Sunnah (definition), if someone forgets it and starts Al-Fatihah, he should not go back to it because it is a Sunnah whose time has passed, even though some view it permissible to go back to it.