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 الْعَلاَءِ، قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، قَالَ حَدَّثَنَا الأَعْمَشُ، عَنْ شَقِيقٍ، عَنْ عَبْدِ اللَّهِ، قَالَ أَوَّلُ مَا يُقْضَى بَيْنَ النَّاسِ فِي الدِّمَاءِ .
It was narrated that 'Abdullah said: "The first matter concerning which scores will be settled among the people will be bloodshed."
Reference : Sunan an-Nasa'i 3996In-book reference : Book 37, Hadith 31English translation : Vol. 5, Book 37, Hadith 4001