Sunan an Nasai 5056
The Book of Adornment
أَخْبَرَنَا مُحَمَّدُ بْنُ بَشَّارٍ، قَالَ حَدَّثَنَا أَبُو دَاوُدَ، قَالَ حَدَّثَنَا حَمَّادُ بْنُ سَلَمَةَ، عَنْ قَتَادَةَ، عَنِ الْحَسَنِ، أَنَّ النَّبِيَّ صلى الله عليه وسلم نَهَى عَنِ التَّرَجُّلِ إِلاَّ غِبًّا .
It was narrated from Al-Hasan that:The Prophet [SAW] forbade coming one's hair except 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.