An-Nisa · 4:93

93. If anyone kills a believer, deliberately intending to do so, his recompense will be Hell to live there eternally. Allah will be angry with him, distance him from His mercy, and will prepare for him a great punishment for committing such a serious crime. The belief of the Ahl as-Sunnah wa’l-Jamā’ah is that if the killer is a believing Muslim, he will not literally remain in Hell eternally; but he will be punished in it for a long period and will then be removed from there through Allah’s grace.