The instance where Allah is pleased with both the killer and the one who is killed
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.
أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ يَضْحَكُ اللَّهُ إِلَى رَجُلَيْنِ يَقْتُلُ أَحَدُهُمَا الآخَرَ كِلاَهُمَا يَدْخُلُ الْجَنَّةَ فَقَالُوا كَيْفَ يَا رَسُولَ اللَّهِ قَالَ يُقَاتِلُ هَذَا فِي سَبِيلِ اللَّهِ ﷻ فَيُسْتَشْهَدُ ثُمَّ يَتُوبُ اللَّهُ عَلَى الْقَاتِلِ فَيُسْلِمُ فَيُقَاتِلُ فِي سَبِيلِ اللَّهِ ﷻ فَيُسْتَشْهَدُ