Musnad Abu Ya'la al-Mawsili 160:116

And with his chain of narration, that the Messenger of Allah (may Allah bless him and grant him peace) said: "The Hour will not be established until thirty impostors (dajjals) emerge, all of them claiming that he is the Messenger of Allah; and until knowledge is taken away, tribulations appear, and *al-harj* increases." They said: "O Messenger of Allah, and what is *al-harj*?" He said: "Killing."