Deuteronomy 31:19-22

19Now therefore write ye this song for you, and teach it to the children of Israel: put it in their mouths, that this song may be a witness for me against the children of Israel. 20For when I shall have brought them into the land which I swore to their fathers, that floweth with milk and honey; and they shall have eaten and filled themselves, and grew fat; then will they turn to other gods, and serve them, and provoke me, and break my covenant. 21And it shall come to pass, when many evils and troubles have befallen them, that this song shall testify against them as a witness; for it shall not be forgotten out of the mouths of their seed: for I know their imagination which they frame, even now, before I have brought them into the land which I swore.12

22Moses therefore wrote this song the same day, and taught it to the children of Israel.