" 4.80.1: Narrated Abu Huraira: Allah's Apostle said, "Allah welcomes two men with a smile; one of whom kills the other and both of them enter Paradise. One fights in Allah's Cause and gets killed. Later on Allah forgives the 'killer who also get martyred (In Allah's Cause). "

― محمد بن إسماعيل البخاري , صحيح البخاري