Musnad Ahmad 26:756

Husayn ibn Ali narrated to us, from Za'idah, from Sulayman, from Shaqiq, who said: I was with Abdullah and Abu Musa, and they were talking, and they mentioned from the Messenger of Allah, peace and blessings of Allah be upon him, that he said: "Before the Hour, there are days in which knowledge will be lifted, ignorance will descend, and al-harj will increase." He said: They both said: Al-harj is killing.