The Book of Fighting [The Prohibition of Bloodshed]
37/2. Chapter:
The Gravity of the Sin of Shedding Blood
Sunan an-Nasai
أَخْبَرَنَا مُحَمَّدُ بْنُ عَبْدِ الأَعْلَى، عَنْ خَالِدٍ، حَدَّثَنَا شُعْبَةُ، عَنْ سُلَيْمَانَ، قَالَ سَمِعْتُ أَبَا وَائِلٍ، يُحَدِّثُ عَنْ عَبْدِ اللَّهِ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " أَوَّلُ مَا يُحْكَمُ بَيْنَ النَّاسِ فِي الدِّمَاءِ " .
It was narrated that 'Abdullah said: "The Messenger of Allah [SAW] said: 'The first matter concerning which judgment will be passed among the people will be bloodshed.'"
Reference : Sunan an-Nasa'i 3992In-book reference : Book 37, Hadith 27English translation : Vol. 5, Book 37, Hadith 3997