Musnad Ahmad 26:148

Waki’ narrated to us, Al-A’mash narrated to us, from Abu Wa’il, who said: I was sitting with Abdullah and Abu Musa, and they both said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, before the Hour, there are days in which ignorance will descend, knowledge will be lifted, and *al-harj* will increase." He said: We said: "And what is *al-harj*?" He said: "Killing."