Musnad Ahmad 27:1789

Hajjaj narrated to us, Laith narrated to us, Aqil narrated to us, from Ibn Shihab, from Salim ibn Abdullah, from Abdullah ibn Umar, that the Messenger of Allah (may Allah bless him and grant him peace) stood to deliver a sermon and said: "Behold, indeed the tribulation is from here, from where the horn of Satan rises," meaning the East.