Sunan an-Nasa'i, Hadith 3996 ⓘ
It was narrated that 'Abdullah said: "The first matter concerning which scores will be settled among the people will be bloodshed."
أَخْبَرَنَا مُحَمَّدُ بْنُ الْعَلاَءِ، قَالَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، قَالَ حَدَّثَنَا الأَعْمَشُ، عَنْ شَقِيقٍ، عَنْ عَبْدِ اللَّهِ، قَالَ أَوَّلُ مَا يُقْضَى بَيْنَ النَّاسِ فِي الدِّمَاءِ .
also referenced under: Book 37, Hadith 31 (In-Book) & Volume 5, Book 37, Hadith 4001 (DarusSalam)