Sahih al-Bukhari 5888
صحيح البخاري#5888SahihNarrated Ibn `Umar:The Prophet (ﷺ) said, "To get the moustaches cut 'short is characteristic of the Fitra
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 77:105