Sunan an-Nasa'i 4023
سنن النسائي#4023Sahihأَخْبَرَنَا مُحَمَّدُ بْنُ قُدَامَةَ، قَالَ حَدَّثَنَا جَرِيرٌ، عَنْ زَيْدِ بْنِ عَطَاءِ بْنِ السَّائِبِ، عَنْ زِيَادِ بْنِ عِلاَقَةَ، عَنْ أُسَامَةَ بْنِ شَرِيكٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " أَيُّمَا رَجُلٍ خَرَجَ يُفَرِّقُ بَيْنَ أُمَّتِي فَاضْرِبُوا عُنُقَهُ " .
It was narrated that Usamah bin Sharik said:"The Messenger of Allah [SAW] said: 'Any man who goes out and tries to create division among my Ummah, strike his neck (kill him)
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Abu GhuddahSahih Lighairihi
Al-AlbaniSahih
Zubair Ali ZaiHasan
In-book reference: 37:58