كتاب الإمارة
33
The Book on Government
(14)
Chapter: The ruling on one who seeks to divide the muslims when they are united
(14)
باب حُكْمِ مَنْ فَرَّقَ أَمْرَ الْمُسْلِمِينَ وَهُوَ مُجْتَمِعٌ ‏‏

It has been narrated on the authority of 'Arfaja who said:

I have heard the Messenger of Allah (ﷺ) say: Different evils will make their appearance in the near future. Anyone who tries to disrupt the affairs of this Umma while they are united you should strike him with the sword whoever he be. (If remonstrance does not prevail with him and he does not desist from his disruptive activities, he is to be killed.)
حَدَّثَنِي أَبُو بَكْرِ بْنُ نَافِعٍ ، وَمُحَمَّدُ بْنُ بَشَّارٍ ، قَالَ ابْنُ نَافِعٍ : حَدَّثَنَا غُنْدَرٌ ، وقَالَ ابْنُ بَشَّارٍ : حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ ، حَدَّثَنَا شُعْبَةُ ، عَنْ زِيَادِ بْنِ عِلَاقَةَ ، قَالَ : سَمِعْتُ عَرْفَجَةَ ، قَالَ : سَمِعْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ ، يَقُولُ : " إِنَّهُ سَتَكُونُ هَنَاتٌ وَهَنَاتٌ ، فَمَنْ أَرَادَ أَنْ يُفَرِّقَ أَمْرَ هَذِهِ الْأُمَّةِ وَهِيَ جَمِيعٌ ، فَاضْرِبُوهُ بِالسَّيْفِ كَائِنًا مَنْ كَانَ "
Reference : Sahih Muslim 1852 a
In-book reference : Book 33, Hadith 93
USC-MSA web (English) reference : Book 20, Hadith 4565
  (deprecated numbering scheme)