'Abdullah Ibn Mas'ud (RAA) narrated that The Messenger of Allah (ﷺ) said:
"The first issues to be judged among people on the Day of Resurrection, are those of unlawful blood-shed." Agreed upon. (DE)
English reference (DE): Book 9, Hadith 1201 (DE)
Arabic reference (DE): Book 9, Hadith 1171 (DE)