Sunan an Nasai 5057
The Book of Adornment
أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا بِشْرٌ، عَنْ يُونُسَ، عَنِ الْحَسَنِ، وَمُحَمَّدٍ، قَالاَ التَّرَجُّلُ غِبٌّ .
It was narrated that Al-Hasan and Muhammad said:"Combing one's hair (should be done) every other day
Grading: Abu Ghuddah: Sahih Lighairihi · Al-Albani: Sahih · Zubair Ali Zai: Daif
Text from the public-domain hadith-api dataset. Numbering follows that dataset and can differ by a few from some printed editions — check the wording, not only the number.