Musannaf Ibn Abi Shayba 32:20

Abdullah ibn Numayr narrated to us, from Malik ibn Mighwal, who said: It was written in the Zabur (Psalms) of David: "Indeed, I am Allah; there is no god but Me. I am the King of kings. The hearts of kings are in My hand. So, whichever people are in obedience to Me, I make the kings a mercy upon them. And whichever people are in disobedience to Me, I make the kings a vengeance upon them. Do not occupy yourselves with the cause of kings, and do not repent to them. Repent to Me, and I will incline their hearts toward you."