It has been narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:God laughs at the two men both of whom will enter Paradise (though) one of them kills the other. They said: Messenger of Allah, how is it? He said: One of them fights in the way of Allah, the Almighty and Exalted. and dies a martyr. Then God turns in mercy to the murderer who embraces Islam, fights in the way of Allah, the Almighty and Exalted, and dies a martyr

English translation · Sahih Muslim