One of the recommended acts which Islam has emphasized upon is cutting of nails in whatever manner or way it may be. Cutting of nails on Friday is better and it is also better to start cutting the nails with the left hand little finger and finish up with the right hand little finger. It is permissible to cut the nails at any time of the day or night. Based on the research we have conducted, we did not find any narration on abominableness of cutting nails at night. Hence, it is meaningless to take up a discussion regarding the alleged abominableness.
One of the recommended acts which Islam has emphasized upon is cutting of nails. The jurists and religious scholars discussed it in their books. For instance, Sayyid Sabzevari says in his Muhazzab al-Ahkam: It is recommended to cut the nails, and not cutting them and leaving them long are abominable because Imam Sadiq (as) says: “Cutting of nails is Sunnah and recommended.” As well, the Imam (as) has been narrated as having said: “Verily the most hidden and subtle way that Satan has managed to gain control over man is that he has made himself an abode under his nails.” It is makrooh (abominable) to cut your nails with your teeth. Imam Sadiq (as) narrates from his forefathers that the Holy Prophet (s) forbade cutting of the nails with the teeth: “The Prophet of Islam (s) forbade from cutting of nails with the teeth and also hijamat (cupping) on the nights preceding Wednesday and Friday.” It is recommended to cut nails on any day. Musa bin Bakr narrates from Imam Sadiq (as) that someone said to the Imam that Shiites were saying that cutting back moustache and trimming of nails should be on Friday. Imam Sadiq (as) said: “God is Glorified. You are free to cut them on Fridays or on any other days.” Of course, it is better to cut the nails on Fridays. Ibn Senan narrates from Imam Sadiq (as) that he said: “He who cuts back his moustache and trims his nails and washes his head with marshmallow ( the plant), he has earned the reward of setting a slave free.” He also said: According to Imam al-Sadiq (a.s): "Trimming the nails, cutting back the moustache and washing the head with marshmallow on Fridays, precludes poverty and increases the income."
According to Imam Baqir (a.s): "When you trim your nails on Friday, start with the left little finger and finish up with the right little finger."
The conclusion is that it is permissible to cut the nails at any time of the day and night. Based on the research we have conducted, we did not find any narration on the purported abominableness of cutting nails at night. Hence, it is meaningless to take up a discussion regarding abominableness of cutting nails.
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 Hurr Amili, Wasail al-Shi’ah, vol.2, chapter (Aadab al-Hammam) “The Bathroom Manners ”, hadith 4, Aalulbayt Institute, Qom, 1409
 Ibid, p. 134, hadith 1.
 Ibid, p. 133, hadith 6.
 Kulayni, Al-Kafi, vol.3, p. 418, Dar al-Kutub al-Islamiyah, Tehran, 1365 A.H. (1976); Wasail al-Shia, vol.7, p. 354, chapt. 32, Friday Prayer and Its Manners, hadith 2.
 Wasail al-Shia, vol.2, p. 60 – 62, chapter 32, Friday Prayer and Its Manners, hadith 3; Kulayni, Al-Kafi, vol.3, p. 418.
 Makarim al-Akhlaq pp.66. See also Majalisi, Muhammad Baqir, Behar al-Anwar, vol.59, p. 268, Al-Wafa Institute, Beirut, Lebanon, 1404 A.H.; Al-Sabzevari, Al-Sayyid Abdul A’laa, Muhazzab al-Ahkam fi Bayan al-Halal wal-Haram, vol.4, p. 483 – 484, fourth edition, Qom, Office of Ayatollah Sayyid Sabzevari, 1413 A.H.