When Did Israel First Expect Deliverance from Egypt?

When one watches the 1955 epic, *The Ten Commandments,* one gets the impression that enslaved Israel had been expecting God to send a deliverer for four hundred years. Is this true? A promise is given by God in Ex. 3,17: > And I have said the word to bring you forth out of the affliction of Egypt, into the land of the Chanaanite, the Hethite, and the Amorrhite, and Pherezite, and Hevite, and Jebusite, to a land that floweth with milk and honey. (Douay-Rheims) But there, God is already speaking to Moses. When and where is Israel's deliverance from Egypt first prophesied? Had they been expecting a deliverer for four hundred years?