Musannaf Ibn Abi Shayba 18:1224

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Al-A’mash narrated to us, from Abu Wa’il, from ‘Abdullah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The first thing that will be judged between people on the Day of Resurrection is [regarding] bloodshed."