It 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.'"
أَخْبَرَنَا أَبُو عَلِيٍّ، مُحَمَّدُ بْنُ عَلِيٍّ الْمَرْوَزِيُّ قَالَ حَدَّثَنَا عَبْدُ اللَّهِ بْنِ عُثْمَانَ، عَنْ أَبِي حَمْزَةَ، عَنْ زِيَادِ بْنِ عِلاَقَةَ، عَنْ عَرْفَجَةَ بْنِ شُرَيْحٍ، قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم " إِنَّهَا سَتَكُونُ بَعْدِي هَنَاتٌ وَهَنَاتٌ وَهَنَاتٌ - وَرَفَعَ يَدَيْهِ - فَمَنْ رَأَيْتُمُوهُ يُرِيدُ تَفْرِيقَ أَمْرِ أُمَّةِ مُحَمَّدٍ صلى الله عليه وسلم وَهُمْ جَمِيعٌ فَاقْتُلُوهُ كَائِنًا مَنْ كَانَ مِنَ النَّاسِ " .
Nesai
The Book of Fighting [The Prohibition of Bloodshed] • Hadith 4021