Sunan an-Nasa'i, Book 48, Hadith 18 (In-Book) ⓘ
It was narrated that Al-Hasan and Muhammad said: "Combing one's hair (should be done) every other day."
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا بِشْرٌ، عَنْ يُونُسَ، عَنِ الْحَسَنِ، وَمُحَمَّدٍ، قَالاَ التَّرَجُّلُ غِبٌّ .
also referenced under: Hadith 5057 (Reference) & Volume 6, Book 48, Hadith 5060 (DarusSalam)