Deuteronomy 17:16-20

16Moreover, he must not accumulate horses for himself or allow the people to return to Egypt to do so, for the Lord has said you must never again return that way.

17Furthermore, he must not marry many wives lest his affections turn aside, and he must not accumulate much silver and gold.

18When he sits on his royal throne he must make a copy of this law on a scroll given to him by the Levitical priests.

19It must be with him constantly and he must read it as long as he lives, so that he may learn to revere the Lord his God and observe all the words of this law and these statutes and carry them out.

20Then he will not exalt himself above his fellow citizens or turn from the commandments to the right or left, and he and his descendants will enjoy many years ruling over his kingdom in Israel.