Short answer
Growing your nails long goes against the Sunnah. Cutting the nails is part of the fitrah, and the Companions were told not to leave them more than 40 days, so in the Hanafi school leaving them uncut beyond 40 days is makruh tahrimi. Keeping them slightly long but trimmed within that limit is not a sin. The rule is the same for women and men.
Trimming the nails is sunnah, ideally weekly, and leaving them uncut beyond 40 days is makruh tahrimi. Ordinary grime under the nails does not spoil wudu, but anything that forms a layer on the nail, such as dough, paint or glue, does.
The four schools agree on this.
Explanation
The Prophet ﷺ named cutting the nails among the five practices of the fitrah (the natural way). Anas said the Companions were given a limit of 40 nights for trimming the moustache, cutting the nails and removing body hair. The scholars took this as the outer limit, with weekly trimming as the best practice. See the Sunnah way of cutting nails.
Long nails as fashion. Long, shaped nails are a beauty trend, but they work against the fitrah. Nails grown for months, or filed into claws, collect dirt and germs and make cooking, istinja and caring for children less clean. Hanafi muftis therefore advise women to keep their nails short or only slightly long, and never to pass 40 days without trimming.
Wudu. The Hanafi texts say ordinary grime under the nails does not stop wudu, because people cannot always avoid it. Dough, paint, wax or glue does block water and must be removed, and long nails trap these more easily, so check them before you pray. Polish and artificial nails are covered in are fake nails haram.
Practical points. Trim on Friday if you can, and do not let 40 days pass. If you work in healthcare or with food, short nails are often required anyway, which fits the Sunnah. There is no sin in nails that are a little long, as long as they are clean and trimmed within the limit. The other schools also teach the 40-day limit.
The evidence
Quran, Surah Al-Baqara 2:222
وَيَسْـَٔلُونَكَ عَنِ ٱلْمَحِيضِ ۖ قُلْ هُوَ أَذًۭى فَٱعْتَزِلُوا۟ ٱلنِّسَآءَ فِى ٱلْمَحِيضِ ۖ وَلَا تَقْرَبُوهُنَّ حَتَّىٰ يَطْهُرْنَ ۖ فَإِذَا تَطَهَّرْنَ فَأْتُوهُنَّ مِنْ حَيْثُ أَمَرَكُمُ ٱللَّهُ ۚ إِنَّ ٱللَّهَ يُحِبُّ ٱلتَّوَّٰبِينَ وَيُحِبُّ ٱلْمُتَطَهِّرِينَ ﴿٢٢٢﴾
And they ask you about menstruation. Say, "It is harm, so keep away from wives during menstruation. And do not approach them until they are pure. And when they have purified themselves, then come to them from where Allah has ordained for you. Indeed, Allah loves those who are constantly repentant and loves those who purify themselves."
Allah loves cleanliness, which the practices of the fitrah serve.
Sahih al-Bukhari 5891
Sahih... الفطرة خمس الختان والاستحداد وقص الشارب وتقليم الأظفار ...
"Five things are part of the fitrah: circumcision, shaving the pubic hair, trimming the moustache, cutting the nails..."
Cutting the nails is part of the natural way.
Sahih Muslim 258
Sahih... وقت لنا في قص الشارب وتقليم الأظفار ونتف الإبط وحلق العانة أن لا نترك أكثر من أربعين ليلة ...
"We were given a time limit for trimming the moustache, cutting the nails, plucking the armpits and shaving the pubic hair: not to leave them more than forty nights."
The 40-day limit.
Where the ruling is recorded
- al-Fatawa al-Hindiyya, Kitab al-Karahiyya, chapter on circumcision, hair and nails. Weekly trimming is best, fifteen days is the middle, forty days is the outer limit, and leaving it beyond forty deserves the warning.
- al-Durr al-Mukhtar with Radd al-Muhtar, Kitab al-Taharah, the obligations of wudu. Grime under the nails does not prevent wudu, while dough and similar substances do.
Checked by our team. For a more accurate answer to your own situation, consult a scholar. Quran translation by Sahih International. Hadith Arabic from the standard editions of the six books and the Muwatta, with gradings as recorded there; the English is our own rendering. Spotted a mistake? Tell us.