The Prophet ﷺ said, "When two Muslims meet with their swords drawn against each other, both the killer and the killed are in the Fire."
حدثنا سويد بن سعيد حدثنا مبارك بن سحيم عن عبد العزيز بن صهيب
عن النبي ﷺ قال ما من مسلمين التقيا بأسيافهما إلا كان القاتل والمقتول في النار
No references are available.
[Sahih] Busiri graded it daif because of Mubarak bin Suhaym, but it has corroborating narrations, including the following hadith and the one after it.