Musnad Ahmad 30:3824

Kathir ibn Hisham narrated to us, Ja'far narrated to us, Yazid ibn al-Asamm narrated to us, he said: I heard Abu Hurairah saying: The Prophet of Allah, may Allah bless him and grant him peace, said: "Tribulations will appear, and al-harj will increase." We said: "And what is al-harj?" He said: "Killing, killing." He said: "And knowledge will be taken away."