Reference: Fataawa Noor 'alad-Darb q5624 p77 v11
Question: What is the ruling regarding women letting their nails grow long, and is that permissible?
Response: With respect to both women and men who grow their nails long, then this is in [direct] opposition to the natural disposition upon which Allaah created mankind, as the Prophet ﷺ has stipulated a time for his ummah [to trim] the nails and the moustache, and [to shave] the hair under the armpits as well as around the pubic region - and that it should not be more than forty days [transmitted by Muslim no.258]. And this [narration] has been authentically reported from the Prophet ﷺ, so both the women and the men must not allow their nails to grow long - and certainly not allow forty days to pass [without cutting them].
