Deuteronomy 31:19-22

19“Now therefore, write down this song for yourselves, 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.

20When I have brought them to the land flowing with milk and honey, of which I swore to their fathers, and they have eaten and filled themselves and grown fat, then they will turn to other gods and serve them; and they will provoke Me and break My covenant.

21Then it shall be, when many evils and troubles have come upon them, that this song will testify against them as a witness; for it will not be forgotten in the mouths of their descendants, for I know the inclination of their behavior today, even before I have brought them to the land of which I swore to give them.”

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