As far as Islamic Shari`ah is concerned, there is nothing wrong in brushing one’s hair or clipping nails at nighttime. There is nothing in the authentic Islamic sources to the effect that such acts are forbidden at night.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states: There is nothing in the authentic Islamic sources that suggests either explicitly or implicitly that brushing one’s hair or clipping nails is forbidden at nighttime. It is simply a cultural construction. It behooves us to know that in Islam we are not allowed to declare things halal (lawful) or haram (unlawful) based on our whims and caprices; we must do so based only on the explicit or implicit evidences of the Revelation. Allah says: (And do not say, as to what your tongue falsely describes, “This is lawful, and this is forbidden,” in order to forge a falsehood about Allah. Those who forge falsehoods about Allah never succeed) (Ar-Ra`d 13: 116).
In light of the above, there is nothing in Islam to declare brushing or clipping one’s nail at night as forbidden.