Deuteronomy 17:15-18

15you are to appoint over yourselves the king whom the LORD your God shall choose. Appoint a king from among your brothers; you are not to set over yourselves a foreigner who is not one of your brothers.

16But the king must not acquire many horses for himself or send the people back to Egypt to acquire more horses, for the LORD has said, ‘You are never to go back that way again.’ 17He must not take many wives for himself, lest his heart go astray. He must not accumulate for himself large amounts of silver and gold.

18When he is seated on his royal throne, he must write for himself a copy of this instruction on a scroll in the presence of the Levitical priests.