The Messenger of Allah ﷺ said, "A disbeliever and the one who killed him will never come together in the Fire."
وبهذا الإسناد أن رسول الله ﷺ قال لا يجتمع كافر وقاتله في النار أبدا
Its chain of transmission is sahih. It occurred previously at 8801, and it was narrated by Muslim 3/1505 no. 1891, in the chapter on leadership, on one who kills a disbeliever and then remains steadfast, and by Abu Dawud 3/7 no. 2495. Hakim graded it sahih in Al-Mustadrak 2/72, and Dhahabi agreed with him.