Arfajah bin Shuraih (RAA) narrated, ‘I heard the Messenger of Allah (ﷺ) say, “He who comes to you when you are united and wants to disunite your community, kill him.” Related by Muslim.

وَعَنْ عَرْفَجَةَ بْنِ شُرَيْحٍ: سَمِعْتُ رَسُولَ اَللَّهِ ‏- صلى الله عليه وسلم ‏-يَقُولُ: { مَنْ أَتَاكُمْ وَأَمَرَكُمْ جَمِيعٌ, يُرِيدُ أَنْ يُفَرِّقَ جَمَاعَتَكُمْ, فَاقْتُلُوهُ } أَخْرَجَهُ مُسْلِمٌ .‏ [1]‏ .‏