What is the ruling on letting the nails grow long?

Question 9: What is the ruling on letting the nails grow long?

Answer: It is not permissible to let one’s nails grow long because it is against Sunan al-Fitrah (natural hygiene) which the Prophet (peace upon him) has exhorted us to adhere to. Clipping the nails is one of Sunan al-Fitrah, which also include plucking the armpit hair, shaving the pubic hair, and cutting the moustache short; and this should be done at most every forty days, according to the Hadeeth related by Muslim in his Saheeh (Authentic Hadeeth Book) on the authority of Anas (may Allaah be pleased with him) who said... read more here.