Sahih al-Bukhari 5888
صحيح البخاري#5888Sahihحَدَّثَنَا الْمَكِّيُّ بْنُ إِبْرَاهِيمَ، عَنْ حَنْظَلَةَ، عَنْ نَافِعٍ، قَالَ أَصْحَابُنَا عَنِ الْمَكِّيِّ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " مِنَ الْفِطْرَةِ قَصُّ الشَّارِبِ ".
Narrated Ibn `Umar:The Prophet (ﷺ) said, "To get the moustaches cut 'short is characteristic of the Fitra
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:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 77:105