With a loud voice Moses proclaimed the last plague, closing his announcement with the words: "And all these thy servants shall come down unto me and bow down themselves unto me, saying, Get thee out: and all the people that follow thee; and after that I will go out." Moses knew well enough that Pharaoh himself would come and urge him to lead Israel forth with as great haste as possible, but he mentioned only the servants of the king, and not the king himself, because he never forgot the respect due to a ruler.
Pharaoh — Signs and Wonders of Moses
Legends of the Jews 4:320