The Book on Government
33/35. Chapter:
Two Men, one of whom kills the other, and both will enter Paradise
Sahih Muslim
حَدَّثَنَا مُحَمَّدُ بْنُ أَبِي عُمَرَ الْمَكِّيُّ، حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " يَضْحَكُ اللَّهُ إِلَى رَجُلَيْنِ يَقْتُلُ أَحَدُهُمَا الآخَرَ كِلاَهُمَا يَدْخُلُ الْجَنَّةَ " . فَقَالُوا كَيْفَ يَا رَسُولَ اللَّهِ قَالَ " يُقَاتِلُ هَذَا فِي سَبِيلِ اللَّهِ عَزَّ وَجَلَّ فَيُسْتَشْهَدُ ثُمَّ يَتُوبُ اللَّهُ عَلَى الْقَاتِلِ فَيُسْلِمُ فَيُقَاتِلُ فِي سَبِيلِ اللَّهِ عَزَّ وَجَلَّ فَيُسْتَشْهَدُ " .
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.
Reference : Sahih Muslim 1890aIn-book reference : Book 33, Hadith 188USC-MSA web (English) reference : Book 20, Hadith 4658