The Prophet ﷺ said, "When two Muslims raise weapons against each other, they are both standing at the brink of Hellfire. If one kills the other, they will both enter it together."
حدثنا محمد بن بشار حدثنا محمد بن جعفر حدثنا شعبة عن منصور عن ربعي بن حراش
عن النبي ﷺ قال إذا المسلمان حمل أحدهما على أخيه السلاح فهما على جرف جهنم فإذا قتل أحدهما صاحبه دخلاها جميعا
Bukhari narrated it in the chapter on tribulations, section titled "When two Muslims meet with their swords," hadith no. 7083, as a suspended (mualaq) narration from the hadith of Muhammad bin Jafar Ghundar with the same wording. Muslim also narrated it in the chapter on tribulations, section titled "When two Muslims face each other with their swords," hadith no. 2888/16, from Ibn Bashshar with the same wording.