I used my left hand to wash myself after relieving myself, and my fingernails were long. Having performed many prayers later, I found the smell of excrement in my fingernails. I do not know if there were indeed remains of excrement under my fingernails or if it was just the smell. What should I do?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

It is one of the Sunan of the Fitrah (acts of natural disposition) that a Muslim always trims and cleans his fingernails so that filth and odors do not remain there. Being the religion of purification and cleansing, Islam made purification one of the prerequisites of prayer. At the same time, it is the religion of easiness and alleviating hardship.

Consequently, if you cleaned your fingers after making Istinja’ and left no trace of the impurity, or you performed a perfect Wudhoo’ (ablution) where you perfectly cleansed your fingers and only the smell remained, this is pardonable. That is because it is difficult to get rid of the smell unless you use soap or similar cleansing materials. The scholars said: "Things which are difficult to be removed are pardonable." Given that, your prayer is valid and you are not required to repeat it.

If there are remains of excrement under your fingernails and the nails are of a normal length which does not prevent water from reaching the skin, your prayer is valid as well. Nevertheless, it is recommended to repeat the prayer if its due time is not over. That is because when one performs the prayer while he is forgetfully smeared with impurity and then he remembers immediately after ending the prayer with Tasleem (saying: As-salamu ‘alaykum), it is recommended for him to repeat the prayer.  If the fingernails are extraordinarily long and they gather filth and impurities which prevents water from reaching the skin, this prevents the completion and perfection of Wudhoo’. Consequently, the prayer is invalid and it must be repeated after purification.

Al-‘Alawi a Maaliki scholar, said: "Impurities which remain under extraordinarily long fingernails are not pardonable." 

Allaah Knows best.