Are the thoughts that assail a worshiper, casting doubt upon the validity of the message of the Prophet Muhammad, peace and blessings be upon him, considered whispers (waswasah) or a reality, and what is their ruling?

These are only whisperings [waswas] that do not harm their owner as long as he dislikes them and is repulsed by them. They do not affect the validity of the prayer, and he should abandon them and pay them no attention.