It was narrated from Abu Musa Al-Ash'ari that :

The Messenger of Allah ﷺ said: "If two Muslims confront each other with swords and one of them kills the other, then the killer and the slain will both be in Hell." A man said: "O Messenger of Allah, (we understand about) the killer, but what about the one who is killed?" He said: "He wanted to kill his companion."

أَخْبَرَنَا مُجَاهِدُ بْنُ مُوسَى، قَالَ حَدَّثَنَا إِسْمَاعِيلُ، - وَهُوَ ابْنُ عُلَيَّةَ - عَنْ يُونُسَ، عَنِ الْحَسَنِ، عَنْ أَبِي مُوسَى الأَشْعَرِيِّ، أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ " إِذَا تَوَاجَهَ الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَقَتَلَ أَحَدُهُمَا صَاحِبَهُ فَالْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ " . قَالَ رَجُلٌ يَا رَسُولَ اللَّهِ هَذَا الْقَاتِلُ فَمَا بَالُ الْمَقْتُولِ قَالَ " إِنَّهُ أَرَادَ قَتْلَ صَاحِبِهِ " .