Is the pricking sensation a worshiper feels in the anus, due to severe tension, considered to invalidate ablution (wudu), even though there is nothing he intends to expel?

Avoid whispers and doubts, for the best cure for them is to disregard them. Do not repeat ablution due to doubts, for the mentioned tingling does not nullify ablution except with certain conviction of something having exited. As for doubt and whisper, the original state is the persistence of purity and the validity of ablution.