It has been reported on the authority of Abu Huraira that the Messenger of Allah ﷺ said: 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.

حَدَّثَنَا مُحَمَّدُ بْنُ رَافِعٍ، حَدَّثَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنْ هَمَّامِ بْنِ مُنَبِّهٍ، قَالَ هَذَا مَا حَدَّثَنَا أَبُو هُرَيْرَةَ، عَنْ رَسُولِ اللَّهِ ﷺ فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ ﷺ " 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 " .