Deuteronomy 31:2-6

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. The LORD will do to them just as He did to Sihon and Og, the kings of the Amorites, and to their land, when He destroyed them. The LORD will hand them over to you, and you shall do to them in accordance with all the commandments which I have commanded you. Be strong and courageous, do not be afraid or tremble in dread before them, for it is the LORD your God who goes with you. He will not fail you or abandon you.”