Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
Qurʾān Bukhārī Muslim Nasāʾī Abū Dāwūd Tirmidhī Ibn Mājah Mālik Aḥmad Dārimī Ḥākim Ibn Ḥibbān Ṭabarānī Nasāʾī's Kubrá Bayhaqī al-Luʾluʾ wa-al-Marjān Ibn Rajab's Fifty Riyāḍ al-Ṣāliḥīn Aḥmad's Zuhd Suyūṭī
ibnmajah:3963 – Sūwayd b. Saʿīd > Mubārak b. Suḥaym > ʿAbd al-ʿAzīz b. Ṣuhayb > Anas b. Mālik

“There are no two Muslims who confront one another with their swords, but both the killer and the slain will be in Hell.”  

ابن ماجة:٣٩٦٣ – حَدَّثَنَا سُوَيْدُ بْنُ سَعِيدٍ حَدَّثَنَا مُبَارَكُ بْنُ سُحَيْمٍ عَنْ عَبْدِ الْعَزِيزِ بْنِ صُهَيْبٍ عَنْ أَنَسِ بْنِ مَالِكٍ

عَنِ النَّبِيِّ ﷺ قَالَ مَا مِنْ مُسْلِمَيْنِ الْتَقَيَا بِأَسْيَافِهِمَا إِلاَّ كَانَ الْقَاتِلُ وَالْمَقْتُولُ فِي النَّارِ  

See similar narrations below:

Collected by Muslim, Suyūṭī
muslim:2888b – Aḥmad b. ʿAbdah al-Ḍabbī > Ḥammād > Ayyūb And Yūnus Wa-al-Muʿallá b. Ziyād > al-Ḥasan > al-Aḥnaf b. Qays > Abū Bakrah

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

مسلم:٢٨٨٨b – وَحَدَّثَنَاهُ أَحْمَدُ بْنُ عَبْدَةَ الضَّبِّيُّ حَدَّثَنَا حَمَّادٌ عَنْ أَيُّوبَ وَيُونُسَ وَالْمُعَلَّى بْنِ زِيَادٍ عَنِ الْحَسَنِ عَنِ الأَحْنَفِ بْنِ قَيْسٍ عَنْ أَبِي بَكْرَةَ قَالَ

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