Answered by Ustadha Shazia Ahmad
Concerning dirt under the fingernails, I noticed that in the “Reliance”, it mentioned that any speck of dirt was unacceptable. Would this even include minute specks which one can only notice after scrutinizing the fingernails, or does this mean that this is any dirt which is seen at a glance? What is the ruling as I am becoming obsessive about seeing dirt under my fingernails.
The exact wording in the Reliance of the Traveller (e5.26) is, “If dirt under the nails prevents the water (O: of ablution or the purificatory bath from reaching the skin beneath) then the ablution (O: or bath) is not valid.”
I asked this question to my teacher, Shaykh Akram Abd al-Wahhab of Mosul, and he said that seeing a speck of dirt under one’s nails does not necessarily mean that the water was prevented from touching the skin or nail, because it may not prevent water from reaching the skin, so one should not assume that his wudu was invalid.
Therefore, the most reliable position in the Shafi`i school is that if dirt under the nails prevents water from reaching the skin or nails, the wudu is not valid. The position of Imam Ghazali and Imam Juwayni, however, was that dirt under nails is excused for the purposes of wudu. Many late scholars of the Shafi`i school have given fatwa on this position and it is permissible for one to follow.”
So, in this case, one should not become obsessive about it. First, wudu normally washes away whatever is under the nails of dirt or dust. Secondly, one simply has to glance at one’s hands during wudu and can make a point to clean out his nails if he sees something (after having washed the face), to be on the precautionary side. And finally, if one keeps his nails short, by clipping them every week, or as often as he needs, there is a much higher probability that his nails will be free of anything that prevents water from reaching the skin or nails.
And Allah knows best.