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 عبيد حدثنا الأعمش عن شقيق قال
قال رسول الله ﷺ أول ما يقضى بين الناس يوم القيامة في الدماء
Its isnad is sahih. Bukhari narrated it in 11:343 and 12:166. It was also narrated by Muslim, Tirmidhi, Nasai, and Ibn Majah, as mentioned in Dhakhair al-Mawarith 4875.