Deuteronomy 17:16-20

16But he shall not multiply horses to himself, nor cause the people to return to Egypt, to the end that he should multiply horses: forasmuch as the LORD hath said to you, Ye shall henceforth return no more that way. 17Neither shall he multiply wives to himself, that his heart may turn not away: neither shall he greatly multiply to himself silver and gold. 18And it shall be, when he sitteth upon the throne of his kingdom, that he shall write him a copy of this law in a book out of that which is before the priests the Levites: 19And it shall be with him, and he shall read in it all the days of his life: that he may learn to fear the LORD his God, to keep all the words of this law and these statutes, to do them: 20That his heart may not be lifted above his brethren, and that he may not turn aside from the commandment, to the right hand, or to the left: to the end that he may prolong his days in his kingdom, he, and his children, in the midst of Israel.