Musnad Ahmad 30:3657

Muhammad ibn Bakr narrated to us, Hanzalah informed us, he said: I heard Salim saying: I heard Abu Hurairah saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "Knowledge will be seized, tribulations will appear, and *al-harj* will increase." It was said: "O Messenger of Allah, and what is *al-harj*?" He said with his hand like this: "Meaning: killing."