Sunnah of the Prophet SAW - Cut your nails

“Five things are part of one’s Fitra…” and the Prophet (pbuh) mentioned that trimming the nails is one of them.

[Muslim]

In a hadith by Imam Muslim, the Prophet (pbuh) stated that we should not leave the acts of Fitra [natural disposition] for more than 40 days, as that is a lack of hygiene. We should try to keep our nails reasonably short at all times to prevent dirt from going underneath them.