Sahih al-Bukhari, Volume 9, Book 83, Hadith 4 (USC-MSA) ⓘ
Narrated `Abdullah: The Prophet said, "The first cases to be decided among the people (on the Day of Resurrection) will be those of blood-shed."
حَدَّثَنَا عُبَيْدُ اللَّهِ بْنُ مُوسَى، عَنِ الأَعْمَشِ، عَنْ أَبِي وَائِلٍ، عَنْ عَبْدِ اللَّهِ، قَالَ قَالَ النَّبِيُّ صلى الله عليه وسلم " أَوَّلُ مَا يُقْضَى بَيْنَ النَّاسِ فِي الدِّمَاءِ " .
also referenced under: Book 87, Hadith 4 (In-Book) & Hadith 6864 (DarusSalam)