ENOfficial
It was narrated from Abu Bakrah that the Prophet (ﷺ) said: “When one Muslim wields his weapon against his brother, both of them are at the edge of Hell, and if one of them kills the other, they will both enter it.”
Source: sunnah.com
Other translations
Arabic
حَدَّثَنَا مُحَمَّدُ بْنُ بَشَّارٍ، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ مَنْصُورٍ، عَنْ رِبْعِيِّ بْنِ حِرَاشٍ، عَنْ أَبِي بَكْرَةَ، عَنِ النَّبِيِّ ـ صلى الله عليه وسلم ـ قَالَ " إِذَا الْمُسْلِمَانِ حَمَلَ أَحَدُهُمَا عَلَى أَخِيهِ السِّلاَحَ فَهُمَا عَلَى جُرُفِ جَهَنَّمَ فَإِذَا قَتَلَ أَحَدُهُمَا صَاحِبَهُ دَخَلاَهَا جَمِيعًا " .
sunnah.com