The Messenger of Allah ﷺ said, "The first matter to be judged between people on the Day of Judgment will concern bloodshed."
أخبرنا محمد بن عبد الأعلى عن خالد حدثنا شعبة عن سليمان قال سمعت أبا وائل يحدث
أن رسول الله ﷺ قال أول ما يحكم بين الناس في الدماء
No references are available.
Source reference. Muslim narrated it in the Book of Qasamah, Chapter on Retribution for Bloodshed in the Hereafter, etc., hadith no. 1678, from the hadith of Shubah. And Bukhari narrated it in the Book of Diyat, Chapter on the Words of Allah Most High, "And whoever kills a believer intentionally, his recompense is Hell", hadith no. 6864, from the hadith of Sulayman Amash, through him. It is also found in the Kubra, hadith no. 3454.