Musnad Abu Ya'la al-Mawsili 159:75

And with his chain of narration, he said: The Messenger of Allah, may Allah bless him and grant him peace, said: "The Hour will not be established until knowledge is taken away, ignorance increases, tribulations appear, time draws near, and *al-harj* increases." They said: "And what is *al-harj*, O Messenger of Allah?" He said: "It is killing, killing."