Sahih (Sahih Muslim)
وَحَدَّثَنِي عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا يُونُسُ بْنُ أَبِي يَعْفُورٍ، عَنْ أَبِيهِ، عَنْ عَرْفَجَةَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " مَنْ أَتَاكُمْ وَأَمْرُكُمْ جَمِيعٌ عَلَى رَجُلٍ وَاحِدٍ يُرِيدُ أَنْ يَشُقَّ عَصَاكُمْ أَوْ يُفَرِّقَ جَمَاعَتَكُمْ فَاقْتُلُوهُ " .
It has been narrated (through a still different chain of transmitters) on the Same authority (i. e. 'Arfaja) who said similarly-but adding:" Kill all of them." I heard the Messenger of Allah (ﷺ) say: When you are holding to one single man as your leader, you should kill who seeks to undermine your solidarity or disrupt your unity