Sahih Muslim Book - 52, Hadith - 7252

حَدَّثَنِى أَبُو كَامِلٍ فُضَيْلُ بْنُ حُسَيْنٍ الْجَحْدَرِىُّ حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ عَنْ أَيُّوبَ وَيُونُسَ عَنِ الْحَسَنِ عَنِ الأَحْنَفِ بْنِ قَيْسٍ قَالَ خَرَجْتُ وَأَنَا أُرِيدُ هَذَا الرَّجُلَ فَلَقِيَنِى أَبُو بَكْرَةَ فَقَالَ أَيْنَ تُرِيدُ يَا أَحْنَفُ قَالَ قُلْتُ أُرِيدُ نَصْرَ ابْنِ عَمِّ رَسُولِ اللَّهِ -صلى الله عليه وسلم- - يَعْنِى عَلِيًّا - قَالَ فَقَالَ لِى يَا أَحْنَفُ ارْجِعْ فَإِنِّى سَمِعْتُ رَسُولَ اللَّهِ -صلى الله عليه وسلم- يَقُولُ « إِذَا تَوَاجَهَ الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَالْقَاتِلُ وَالْمَقْتُولُ فِى النَّارِ ». قَالَ فَقُلْتُ أَوْ قِيلَ يَا رَسُولَ اللَّهِ هَذَا الْقَاتِلُ فَمَا بَالُ الْمَقْتُولِ قَالَ « إِنَّهُ قَدْ أَرَادَ قَتْلَ صَاحِبِهِ ».

It was narrated that Al-Ahnaf bin Qais said: "I went out looking for this man, and I was met by Abu Bakrah who said: 'Where are you going, O Ahnaf?' I said: 'I want to support the cousin of the Messenger of Allah (s.a.w) meaning 'Ali. He said to me: 'O Ahnaf, go back, for I heard the Messenger of Allah (s.a.w) say: "When two Muslims confront one another with their swords, the slayer and the slain will both be in the fire." I said - or it was said: - O Messenger of Allah, (we understood about) the slayer, but what about the slain?" He said: "He wanted to kill his companion."