Sahih al-Bukhari 3608
صحيح البخاري#3608SahihNarrated Abu Huraira:Allah's Messenger (ﷺ) said, "The Day of (Judgment) will not be established till there is a war between two groups whose claims (or religion) will be the same
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: 61:115