The Messenger of Allah ﷺ said, "The first matter to be judged among people on the Day of Resurrection will be cases of bloodshed."
حدثنا محمد بن عبد الله بن نمير وعلي بن محمد ومحمد بن بشار قالوا حدثنا وكيع حدثنا الأعمش عن شقيق
قال رسول الله ﷺ أول ما يقضى بين الناس يوم القيامة في الدماء
Bukhari narrated it in the Book of Riqaq, chapter "Retribution on the Day of Resurrection," Hadith: 6533, 6864, from the hadith of Amash, with this wording. And Muslim narrated it in the Book of Qasamah and Combatants, chapter "Retribution for blood in the afterlife, and that it is the first matter to be judged between people on the Day of Resurrection," Hadith: 1678, from Ibn Numayr, with this wording.