Deuteronomy 17:15-16

15Thou shalt surely set him king over thee, whom the LORD thy God shall choose: one from among thy brethren shalt thou set king over thee: thou mayest not set a stranger over thee, who is not thy brother. 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.