ENOfficial
Usama b. Sharik reported God’s Messenger as saying, “Cut off the head of any man who goes out and causes division among my people.” Nasa’i transmitted it.
Source: sunnah.com
Other translations
Arabic
عَن أُسَامَةَ بْنِ شَرِيكٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «أَيُّمَا رَجُلٍ خَرَجَ يُفَرِّقُ بَيْنَ أُمَّتِي فَاضْرِبُوا عُنُقَهُ» . رَوَاهُ النَّسَائِيُّ
sunnah.com