Musannaf Ibn Abi Shayba 33:35

Abdullah ibn Numayr narrated to us, from Malik ibn Mighwal, who said: It was in the Zabur (Psalms) of David: "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, I make the kings a mercy upon them; and whichever people are in disobedience, I make the kings a vengeance upon them. Do not occupy yourselves with the cause of the kings, and do not repent to them. Repent to Me, and I will incline the hearts of the kings toward you."