Sunan an-Nasa'i, Hadith 4020 ⓘ
It was narrated that 'Arfajah bin Shuraih Al-Ashja'I said: "I saw the Prophet [SAW] on the Minbar addressing the people. He said: 'After me there will be many calamities and much evil behavior. Whoever you see splitting away from the Jama'ah or trying to create division among the Ummah of Muhammad [SAW], then kill him, for the Hand of Allah is with the Jama'ah, and the Shaitan is with the one who splits away from the Ummah, running with him.'"
أَخْبَرَنِي أَحْمَدُ بْنُ يَحْيَى الصُّوفِيُّ، قَالَ حَدَّثَنَا أَبُو نُعَيْمٍ، قَالَ حَدَّثَنَا يَزِيدُ بْنُ مَرْدَانْبَهْ، عَنْ زِيَادِ بْنِ عِلاَقَةَ، عَنْ عَرْفَجَةَ بْنِ شُرَيْحٍ الأَشْجَعِيِّ، قَالَ رَأَيْتُ النَّبِيَّ صلى الله عليه وسلم عَلَى الْمِنْبَرِ يَخْطُبُ النَّاسَ فَقَالَ " إِنَّهُ سَيَكُونُ بَعْدِي هَنَاتٌ وَهَنَاتٌ فَمَنْ رَأَيْتُمُوهُ فَارَقَ الْجَمَاعَةَ أَوْ يُرِيدُ تَفْرِيقَ أَمْرِ أُمَّةِ مُحَمَّدٍ صلى الله عليه وسلم كَائِنًا مَنْ كَانَ فَاقْتُلُوهُ فَإِنَّ يَدَ اللَّهِ عَلَى الْجَمَاعَةِ فَإِنَّ الشَّيْطَانَ مَعَ مَنْ فَارَقَ الْجَمَاعَةَ يَرْكُضُ " .
also referenced under: Book 37, Hadith 55 (In-Book) & Volume 5, Book 37, Hadith 4025 (DarusSalam)