The Prophet ﷺ said, "When two Muslims face each other with their swords and one of them kills the other, both of them are in the Fire."Someone asked, "Messenger of Allah, that is the killer, but what of the one who was killed?"He replied, "He too intended to kill his companion."
أخبرني محمد بن إسمعيل بن إبراهيم قال حدثنا يزيد وهو ابن هارون قال أنبأنا سعيد عن قتادة عن الحسن عن أبي موسى الأشعري عن النبي ﷺ قال إذا تواجه المسلمان بسيفيهما فقتل أحدهما صاحبه فهما في النار مثله سواء
[Sahih]. Ibn Majah narrated it from the hadith of Yazid bin Harun, through the same chain (see the previous hadith), and it is also in Kubra, no. 3584.Qatada was corroborated by Yunus bin Ubayd, as will come later, no. 4129.