Is it obligatory to repeat the ablution if a Muslim discovers dirt on one of the limbs of ablution after completing it?

If the dirt present in the nose or on the foot does not prevent water from reaching the skin, then it does not affect the validity of ablution and prayer. If it does prevent water from reaching the skin but is minor, then it does not cause harm, because it is something that commonly occurs. There is no blame on the person afflicted with obsessive thoughts for adopting the easiest of opinions.