Sunan an-Nasa'i, Book 37, Hadith 155 (In-Book) ⓘ
It was narrated from Abu Bakrah that : The Prophet [SAW] said: "If two Muslims confront each other with swords, each of them wanting to kill the other, they will both be in Hell." It was said to him: "O Messenger of Allah, (we understand about) the killer, but what about the one who is killed?" He said: "He was determined to kill his companion."
أَخْبَرَنَا عَلِيُّ بْنُ مُحَمَّدِ بْنِ عَلِيٍّ الْمِصِّيصِيُّ، قَالَ حَدَّثَنَا خَلَفٌ، عَنْ زَائِدَةَ، عَنْ هِشَامٍ، عَنِ الْحَسَنِ، عَنْ أَبِي بَكْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " إِذَا تَوَاجَهَ الْمُسْلِمَانِ بِسَيْفَيْهِمَا كُلُّ وَاحِدٍ مِنْهُمَا يُرِيدُ قَتْلَ صَاحِبِهِ فَهُمَا فِي النَّارِ " . قِيلَ لَهُ يَا رَسُولَ اللَّهِ هَذَا الْقَاتِلُ فَمَا بَالُ الْمَقْتُولِ قَالَ " إِنَّهُ كَانَ حَرِيصًا عَلَى قَتْلِ صَاحِبِهِ " .
also referenced under: Hadith 4120 (Reference) & Volume 5, Book 37, Hadith 4125 (DarusSalam)