Deuteronomy 17:15-16

15thou shalt only set him king over thee whom Jehovah thy 1God will choose: from among thy brethren shalt thou set a king over thee; thou mayest not set a foreigner over thee, who is not thy brother.

16Only he shall not multiply horses to himself, nor lead back the people to Egypt, to multiply horses; for Jehovah hath said unto you, Ye shall not return again any more that way.