Sunan an-Nasa'i 5056
سنن النسائي#5056Sahihأَخْبَرَنَا 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
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih Lighairihi
Al-AlbaniSahih
Zubair Ali ZaiDaif
In-book reference: 48:17