Deuteronomy 17:14-15

14“When you come to the land which the Lord your God is giving you, and possess it and dwell in it, and say, ‘I will set a king over me like all the nations that are around me,’

15you shall surely set a king over you whom the Lord your God chooses; one from among your brethren you shall set as king over you; you may not set a foreigner over you, who is not your brother.