Exodus 12:40-42

Now the period of time the children of Israel lived in Egypt was four hundred and thirty years. [Gen 15:13, 14] At the end of the four hundred and thirty years, to that very day, all the hosts of the LORD [gathered into tribal armies] left the land of Egypt. It is a night of watching to be observed for the LORD for having brought them out of the land of Egypt; this [same] night is for the LORD, to be observed and celebrated by all the Israelites throughout their generations.