Deuteronomy 17:14-18

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.

16But he shall not multiply horses for himself, nor cause the people to return to Egypt to multiply horses, for the Lord has said to you, ‘You shall not return that way again.’

17Neither shall he multiply wives for himself, lest his heart turn away; nor shall he greatly multiply silver and gold for himself.

18“Also it shall be, when he sits on the throne of his kingdom, that he shall write for himself a copy of this law in a book, from the one before the priests, the Levites.