Musnad Abu Ya'la al-Mawsili 153:97

Wasil ibn Abd al-A’la al-Kufi narrated to us, Ibn Fudayl narrated to us, from his father, from Salim, from Ibn Umar, who said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: "Indeed, the tribulation (fitnah) comes from here"—and he gestured with his hand toward the east, where the horn of Satan rises—"and you will strike the necks of one another." "And Moses only killed the one he killed from the people of Pharaoh by mistake. Allah said to him: 'And you killed a person, so We saved you from distress and tried you with a [great] trial' (Ta-Ha: 40)."