Sahih Muslim 1890
Sahih Muslim · Book 33: The Book on Government · Two Men, one of whom kills the other, and both will enter Paradise
It has been reported on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:
حَدَّثَنَا مُحَمَّدُ بْنُ رَافِعٍ ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ ، أَخْبَرَنَا مَعْمَرٌ ، عَنْ هَمَّامِ بْنِ مُنَبِّهٍ ، قَالَ هَذَا مَا حَدَّثَنَا أَبُو هُرَيْرَةَ ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " يَضْحَكُ اللَّهُ لِرَجُلَيْنِ يَقْتُلُ أَحَدُهُمَا الآخَرَ كِلاَهُمَا يَدْخُلُ الْجَنَّةَ " قَالُوا كَيْفَ يَا رَسُولَ اللَّهِ قَالَ " يُقْتَلُ هَذَا فَيَلِجُ الْجَنَّةَ ثُمَّ يَتُوبُ اللَّهُ عَلَى الآخَرِ فَيَهْدِيهِ إِلَى الإِسْلاَمِ ثُمَّ يُجَاهِدُ فِي سَبِيلِ اللَّهِ فَيُسْتَشْهَدُ " .
God laughs at the two men one of whom kills the other; both of them will enter Paradise. They (the Companions) said: How, Messenger of Allah? He said: One is slain (in the way of Allah) and enters Paradise. Then God forgives the other and guides him to Islam; then he fights in the way of Allah and dies a martyr.