The Book of Fighting [The Prohibition of Bloodshed]
37/2. Chapter:
The Gravity of the Sin of Shedding Blood
Sunan an-Nasai
أَخْبَرَنَا يَحْيَى بْنُ حَكِيمٍ الْبَصْرِيُّ، قَالَ حَدَّثَنَا ابْنُ أَبِي عَدِيٍّ، عَنْ شُعْبَةَ، عَنْ يَعْلَى بْنِ عَطَاءٍ، عَنْ أَبِيهِ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لَزَوَالُ الدُّنْيَا أَهْوَنُ عِنْدَ اللَّهِ مِنْ قَتْلِ رَجُلٍ مُسْلِمٍ " .
It was narrated from 'Abdullah bin 'Amr that: The Prophet [SAW] said: "The extinction of the whole world is less significant before Allah than killing a Muslim man."
Reference : Sunan an-Nasa'i 3987In-book reference : Book 37, Hadith 22English translation : Vol. 5, Book 37, Hadith 3992