Musnad Ahmad 30:2400

Yahya narrated to us, from Ibn ‘Ajlan, who said: I heard my father narrating from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The Hour will not be established until knowledge is taken away, ignorance appears, and *al-harj* becomes prevalent." It was said: "And what is *al-harj*?" He said: "Killing."