Deuteronomy 17:16-18

The king, moreover, must not acquire great numbers of horses for himself or make the people return to Egypt to get more of them, for the LORD has told you, “You are not to go back that way again.” He must not take many wives, or his heart will be led astray. He must not accumulate large amounts of silver and gold. When he takes the throne of his kingdom, he is to write for himself on a scroll a copy of this law, taken from that of the Levitical priests.