Is an abundance of doubt the same as an abundance of forgetfulness in prayer or other acts of worship? And what is the guidance for someone who experiences mental wandering during prayer and thinks he has performed a pillar, then a doubt comes to him that he has not performed it, and he forgets that moment, even though he might visualize it and find that he had indeed performed it?

Doubt differs from forgetfulness. Forgetfulness is the act of leaving something due to inattentiveness, while doubt is hesitation between doing something or not doing it. Doubt, according to the jurists, includes hesitation without a preference (technical doubt) and hesitation with a preference for one of the possibilities (presumption and delusion). If doubt becomes excessive, it is considered a whisper (waswasah) that should be disregarded. The person afflicted by these whispers must proceed with their prayer without repeating a pillar or performing the prostration of forgetfulness, because persistent doubt leads to hardship, which is negated in Islamic law.