Musnad Ahmad 27:1842

Ibn Numayr narrated to us, Hanzalah narrated to us, from Salim ibn Abdullah ibn Umar, from Ibn Umar, who said: I saw the Messenger of Allah, peace and blessings of Allah be upon him, gesturing with his hand toward Iraq: "Lo, the tribulation is here. Lo, the tribulation is here," three times, "from where the horn of Satan rises."