Deuteronomy 17:16-20

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. 19It is to remain with him, and he is to read from it all the days of his life, so that he may learn to fear the LORD his God by carefully observing all the words of this instruction and these statutes. 20Then his heart will not be exalted above his countrymen, and he will not turn aside from the commandment, to the right or to the left, in order that he and his sons may reign many years over his kingdom in Israel.