Deuteronomy 17:14-18

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

15you may indeed set a king over you whom the Lord your God will choose. One from among your brothers you shall set as king over you. You may not put a foreigner over you, who is not your brother.

16Only he must not acquire many horses for himself or cause the people to return to Egypt in order to acquire many horses, since the Lord has said to you, 'You shall never return that way again.'

17And he shall not acquire many wives for himself, lest his heart turn away, nor shall he acquire for himself excessive silver and gold.

18"And when he sits on the throne of his kingdom, he shall write for himself in a book a copy of this law, approved by the Levitical priests.