Sahih Muslim 1891
Sahih Muslim · Book 33: The Book on Government · One who kills a disbeliever then keeps to the right path
It has been narrated on the authority of Abu Huraira that the Messenger of Allah (ﷺ) said:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ عَوْنٍ الْهِلاَلِيُّ ، حَدَّثَنَا أَبُو إِسْحَاقَ الْفَزَارِيُّ، إِبْرَاهِيمُ بْنُ مُحَمَّدٍ عَنْ سُهَيْلِ بْنِ أَبِي صَالِحٍ ، عَنْ أَبِيهِ ، عَنْ أَبِي هُرَيْرَةَ ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ يَجْتَمِعَانِ فِي النَّارِ اجْتِمَاعًا يَضُرُّ أَحَدُهُمَا الآخَرَ " . قِيلَ مَنْ هُمْ يَا رَسُولَ اللَّهِ قَالَ " مُؤْمِنٌ قَتَلَ كَافِرًا ثُمَّ سَدَّدَ " .
No two such persons shall be together in Hell as if one of them is such that his presence hurts the other. It was asked: Messenger of Allah, who are they? He said: A believer who killed a disbeliever and (then) kept to the right path."