Sahih al-Bukhari, Volume 8, Book 76, Hadith 540 (USC-MSA) ⓘ
Narrated `Abdullah: The Prophet said, "The cases which will be decided first (on the Day of Resurrection) will be the cases of blood-shedding. "
حَدَّثَنَا عُمَرُ بْنُ حَفْصٍ، حَدَّثَنَا أَبِي، حَدَّثَنَا الأَعْمَشُ، حَدَّثَنِي شَقِيقٌ، سَمِعْتُ عَبْدَ اللَّهِ ـ رضى الله عنه ـ قَالَ النَّبِيُّ صلى الله عليه وسلم " أَوَّلُ مَا يُقْضَى بَيْنَ النَّاسِ بِالدِّمَاءِ " .
also referenced under: Book 81, Hadith 122 (In-Book) & Hadith 6533 (DarusSalam)