What is the ruling on ignoring doubts and whispers in prayer regarding forgetting the Shahada, knowing that these whispers had previously begun?

If one doubts having omitted a pillar (rukn) during prayer, he must perform it. However, if the doubt occurs after completing the prayer, it should be disregarded. If these doubts become frequent and reach the level of obsessive whispers (waswasah), the person afflicted by them should ignore them and not pay them any attention.