The Prophet ﷺ said, "An unbeliever and his Muslim killer will never be gathered together in the Fire."
حدثنا هيثم أخبرنا حفص بن ميسرة عن العلاء عن أبيه
أن النبي ﷺ قال لا يجتمع الكافر وقاتله من المسلمين في النار أبدا
Its isnad is sahih, and it is the same chain as before. Bukhari and Muslim have something similar to it. Bukhari recorded it in the tafsir of Surah Nisa (6/56), Muslim in the Book of Iman (1/164, no. 182), in the chapter on knowing the way of seeing, and Tirmidhi (4/691, no. 2557), in the Book of Paradise, in the chapter on what has been said about the eternity of the people of Paradise.