Sahih Muslim 2458
صحيح مسلم#2458SahihAbu Sa'id al-Khudri reported that the Messenger of Allah (ﷺ) said:A group would secede itself (from the Ummah) when there would be dissension among the Muslims. Out of the two groups who would be nearer the truth would kill them
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih Muslim is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 12:195