Is the dust or dirt accumulated on the body, such as in the navel or under the fingernails (of a blackish color), considered a barrier that prevents the validity of ablution (wudu) or ritual bathing (ghusl) unless removed? And what is the ruling concerning one who performed the ritual bath for menstruation while unaware of the necessity of removing this dust?

If the dirt is solidified and prevents water from reaching the skin, it must be removed for the ablution (ghusl (definition)) and prayer (salat) to be valid, whether it is in the navel or other hidden parts of the body that have the ruling of the outer body. However, a small amount of dirt under the fingernail is excused.

If the dirt is not minimal and covers a large area, it must be removed if it is solidified like clay. As for dirt that does not prevent water from reaching the skin, it does not need to be removed.

If the dirt is ordinary and does not prevent water from reaching the skin, it is not considered a barrier. If it is a small amount, like the barrier under the fingernail, it is forgiven in all parts of the body by analogy with what is under the fingernail.