Sunan an-Nasa'i, Volume 5, Book 37, Hadith 4027 (DarusSalam) ⓘ
It was narrated that 'Arfajah said: "I heard the Messenger of Allah [SAW] say: 'After me there will be many calamities and much evil behavior. Whoever wants to create division among the Ummah (of Muhammad [SAW]) when they are all united, strike him with the sword.'"
أَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، قَالَ حَدَّثَنَا شُعْبَةُ، قَالَ حَدَّثَنَا زِيَادُ بْنُ عِلاَقَةَ، عَنْ عَرْفَجَةَ، قَالَ سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ " سَتَكُونُ بَعْدِي هَنَاتٌ وَهَنَاتٌ فَمَنْ أَرَادَ أَنْ يُفَرِّقَ أَمْرَ أُمَّةِ مُحَمَّدٍ صلى الله عليه وسلم وَهُمْ جَمْعٌ فَاضْرِبُوهُ بِالسَّيْفِ " .
also referenced under: Hadith 4022 (Reference) & Book 37, Hadith 57 (In-Book)