Sahih Muslim 280
صحيح مسلم#280SahihIt is narrated on the authority of Abdullah b. Umar who narrates from the Prophet of Allah (ﷺ) who said:He who took up arms against us is not of us
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: 1:186