Arabic hadith text
وَحَدَّثَنِي عَنْ مَالِكٍ، 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 يُقَاتِلُ هَذَا فِي سَبِيلِ اللَّهِ فَيُقْتَلُ ثُمَّ يَتُوبُ اللَّهُ عَلَى الْقَاتِلِ فَيُقَاتِلُ فَيُسْتَشْهَدُ ‏"‏ ‏.‏
Translation
Yahya related to me from Malik from Abu'z-Zinad from al-Araj fromAbu Hurayra that the Messenger of Allah, may Allah bless him and granthim peace, said, "Allah laughs at two men. One of them kills theother, but each of them will enter the Garden

one fights in the wayof Allah and is killed, then Allah turns to the killer, so he fights(in the way of Allah) and also becomes a martyr."