Musnad Abu Ya'la al-Mawsili 153:156

'Abdullah ibn 'Umar ibn Aban narrated to us, Muhammad ibn Fudayl narrated to us, from his father, who said: I heard Salim ibn 'Abdullah ibn 'Umar saying: "O people of Iraq, why do I ask you about the minor matter and leave you regarding the major matter? I heard my father, 'Abdullah ibn 'Umar, saying: I heard the Messenger of Allah (ﷺ) saying: 'The tribulation will come from here'—and he gestured with his hand toward the east—'and you will be striking the necks of one another.' And Musa (peace be upon him) only killed the one he killed from the family of Pharaoh by mistake. Allah said: 'And you killed a person, so We saved you from distress and tried you with a [severe] trial.'"