Sahih al-Bukhari 6966
صحيح البخاري#6966SahihNarrated `Abdullah bin `Umar:The Prophet (ﷺ) said, "For every betrayer there will be a flag by which he will be recognized on the Day of Resurrection
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: 90:13