Musnad Ahmad 30:3254

Muhammad ibn Ja'far and Rawh narrated to us, they said: 'Awf narrated to us, from Khallas, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The anger of Allah, the Mighty and Majestic, is intense against a man whom His Prophet killed." And Rawh said: "Whom the Messenger of Allah killed, and the anger of Allah is intense against a man who calls himself the King of Kings; there is no king except Allah, the Mighty and Majestic."