Sunan an-Nasa'i 4021
سنن النسائي#4021SahihIt was narrated that 'Arfajah bin Shuraih said:"The Prophet [SAW] said: 'After me there will be many calamities and much evil behavior.' He raised his hands (and said): 'Whomever you see trying to create division among the Ummah of Muhammad [SAW] when they are all united, kill him, no matter who he is among the people
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Abu GhuddahSahih Isnaad
Al-AlbaniSahih Isnaad
Zubair Ali ZaiSahih Muslim
In-book reference: 37:56