D'varim (Deu) 17:14-20

“When you have entered the land ADONAI your God is giving you, have taken possession of it and are living there, you may say, ‘I want to have a king over me, like all the other nations around me.’ In that event, you must appoint as king the one whom ADONAI your God will choose. He must be one of your kinsmen, this king you appoint over you — you are forbidden to appoint a foreigner over you who is not your kinsman. However, he is not to acquire many horses for himself or have the people return to Egypt to obtain more horses, inasmuch as ADONAI told you never to go back that way again. Likewise, he is not to acquire many wives for himself, so that his heart will not turn away; and he is not to acquire excessive quantities of silver and gold. “When he has come to occupy the throne of his kingdom, he is to write a copy of this Torah for himself in a scroll, from the one the cohanim and L’vi’im use. It is to remain with him, and he is to read in it every day, as long as he lives; so that he will learn to fear ADONAI his God and keep all the words of this Torah and these laws and obey them; so that he will not think he is better than his kinsmen; and so that he will not turn aside either to the right or to the left from the mitzvah. In this way he will prolong his own reign and that of his children in Isra’el.