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.
Growing long nails is a clear violation of the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, and his guidance which is the best guidance. The majority of scholars state that clipping the nails is an act of Sunnah and not obligatory, while some scholars, such as Al-Qaadhi Abu Bakr ibn Al-‘Arabi one of the Maaliki scholars, said that it is obligatory as he believes that all the Sunan of Fitrah are obligatory.
The fact that the one in the state of Ihraam is prohibited from clipping his nails does not mean that growing long nails is permissible or lawful as scholars stated that it is permissible for people who are in the state of Ihraam to clip their nails before they assume Ihraam. Moreover, the period of Ihraam is not usually long, so it would not lead the nails to grow long in an excessive way.
Muslims should be diligent to follow the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam, and not to give preference to their own opinion over the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam. They should not be in a state that prevents them from applying the Sunnah of the Prophet, sallallaahu ‘alayhi wa sallam. As for the ruling on the dirt that accumulates under the nail, if it was little, it does not affect the validity of ablution.
Supposing that the duration of the state of Ihraam was prolonged or the person who assumed the state of Ihraam did not clip his nails before assuming Ihraam, it will not be permissible to clip his nails during Ihraam because this is prohibited, while clipping the nails is favorable, and what is prohibited cannot be made permissible because of something favorable. As soon as the person ends the state of Ihraam, it becomes permissible for him to clip his nails. The prohibition of clipping the nails during Ihraam is not a proof of the unfavorability of clipping them in general and no one can quote this as a proof except the one who is totally ignorant.
If the nails grew very long in an abnormal manner, the person should remove the dirt that is under them to be on the safe side and stay away from the differences of opinions among scholars.