Deuteronomy 31:2-3

And he said to them, “I am a hundred and twenty years old today; I am no longer able to come in and go out [as your spiritual and military leader], and the LORD has said to me, ‘You shall not cross this Jordan.’ It is the LORD your God who will cross ahead of you; He will destroy these nations before you, and you shall dispossess them. Joshua is the one who will go across before you [to lead you], just as the LORD has said.