I set out with the intention of helping this person (Hadrat 'Ali) when Abu Bakra met me. He said: Ahnaf, where do you intend to go? I said: I intend to help the cousin of Messenger of Allah ﷺ, viz. 'Ali. Thereupon he said to me: Ahnaf, go back, for I heard Messenger of Allah ﷺ as saying: When two Muslims confront one another with swords (in hand) both the slayer and the slain would be in Fire. He (Ahnaf) said: I said, or it was said: Messenger of Allah, it may be the case of one who kills. but what about the slain (why he would be put in Hell-Fire)? Thereupon he said: He also intended to kill his companion.  

خَرَجْتُ وَأَنَا أُرِيدُ هَذَا الرَّجُلَ فَلَقِيَنِي أَبُو بَكْرَةَ فَقَالَ أَيْنَ تُرِيدُ يَا أَحْنَفُ قَالَ قُلْتُ أُرِيدُ نَصْرَ ابْنِ عَمِّ رَسُولِ اللَّهِ ﷺ يَعْنِي عَلِيًّا قَالَ فَقَالَ لِي يَا أَحْنَفُ ارْجِعْ فَإِنِّي سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ إِذَا تَوَاجَهَ الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَالْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ قَالَ فَقُلْتُ أَوْ قِيلَ يَا رَسُولَ اللَّهِ هَذَا الْقَاتِلُ فَمَا بَالُ الْمَقْتُولِ قَالَ إِنَّهُ قَدْ أَرَادَ قَتْلَ صَاحِبِهِ  

When two Muslims confront each other with their swords, both the slayer and the slain are doomed to Hell-Fire.  

قَالَ رَسُولُ اللَّهِ ﷺ إِذَا الْتَقَى الْمُسْلِمَانِ بِسَيْفَيْهِمَا فَالْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ  

This hadith has been narrated on the authority of Hammad through another chain of transmitters.  

عَنْ أَيُّوبَ بِهَذَا الإِسْنَادِ نَحْوَ حَدِيثِ أَبِي كَامِلٍ عَنْ حَمَّادٍ إِلَى آخِرِهِ  

When two Muslims (confront each other) and the one amongst them attacks his brother with a weapon, both of them are at the brink of Hell-Fire. And when one of them kills his companion, both of them get into Hell-Fire.  

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا الْمُسْلِمَانِ حَمَلَ أَحَدُهُمَا عَلَى أَخِيهِ السِّلاَحَ فَهُمَا فِي جُرُفِ جَهَنَّمَ فَإِذَا قَتَلَ أَحَدُهُمَا صَاحِبَهُ دَخَلاَهَا جَمِيعًا  

The last Hour will not come until the two parties (of Muslims) confront each other and there is a large-scale massacre amongst them and the claim of both of them is the same.  

عَنْ رَسُولِ اللَّهِ ﷺ فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ ﷺ لاَ تَقُومُ السَّاعَةُ حَتَّى تَقْتَتِلَ فِئَتَانِ عَظِيمَتَانِ وَتَكُونُ بَيْنَهُمَا مَقْتَلَةٌ عَظِيمَةٌ وَدَعْوَاهُمَا وَاحِدَةٌ  

The last Hour will not come unless there is much bloodshed. They said: What is harj? Thereupon he said: Bloodshed. bloodshed.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ تَقُومُ السَّاعَةُ حَتَّى يَكْثُرَ الْهَرْجُ قَالُوا وَمَا الْهَرْجُ يَا رَسُولَ اللَّهِ قَالَ الْقَتْلُ الْقَتْلُ