Full Sharh — Mishkat al-Masabih 3395
وَعَنْ أَبِي بَكْرَةَ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «إِذَا الْتَقَى الْمُسْلِمَانِ حَمَلَ أَحَدُهُمَا عَلَى أَخِيهِ السِّلَاحَ فَهُمَا فِي جُرُفِ جَهَنَّمَ فَإِذَا قَتَلَ أَحَدُهُمَا صَاحِبَهُ دَخَلَاهَا جَمِيعًا» . وَفِي رِوَايَةٍ عَنْهُ: قَالَ: «إِذَا الْتَقَى الْمُسْلِمَانِ بسيفهما فَالْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ» قُلْتُ: هَذَا الْقَاتِلُ فَمَا بَالُ الْمَقْتُولِ؟ قَالَ: «إِنَّهُ كَانَ حَرِيصًا عَلَى قَتْلِ صَاحِبِهِ»
English Translation
Abu Bakra reported the Prophet as saying, “When two Muslims meet and one of them bears arms against his brother, they are both on the brink of hell, and if one of them kills the other they will both enter it.” In a version on Abu Bakra's authority he said, “When two Muslims meet with their swords, the one who kills and the one who is killed will go to hell." When he (i.e. Abu Bakr) remarked that one was the killer and asked what was wrong with the one who was killed, he replied, “He was eager to kill his companion." (Bukhari and Muslim.)
Source
Mishkat al-Masabih(مشكاة المصابيح)
Retaliation
Hadith Number
3395