What should I do about the excessive waswasah (whisperings/obsessive thoughts) that afflict me during ablution (wudu’) and prayer (salah), which cause me to repeat the ablution or parts of the prayer repeatedly, even though I am sometimes certain that I have completed them?

Obsessive whispering [Waswasah] has great evil, making its victim seem as if he has no intellect. An example of this is re-reading Al-Fatihah despite being certain of having read it. Previous fatwas have been issued explaining the danger of succumbing to doubt and obsessive whispering, and the ways to prevent them.