מדרש על סנהדרין 43:23

"shall you place over yourself a king": But is it not already written "Place shall you place over yourself a king"? Why, then, "shall you place over yourself a king"? That his awe be over you — whence it was ruled: One is not permitted to ride on his horse or to sit on his throne or to make use of his sceptre or to see him naked or when he is having his hair cut or when he is in the bathhouse.

mishneh": This tells me only of mishneh Torah ("the repetition of the Torah," i.e., the book of Devarim). Whence do I derive (that the mitzvah applies also) to the rest of the Torah? From (Ibid. 19) "to heed all the words of this Torah." If so, why is it written "the mishneh of this Torah"? Because it (i.e., the script) is destined to change (viz. Ezra 4:7 and Daniel 5:8).