Deuteronomy 31:19-22

19"Now therefore write this song and teach it to the people of Israel. Put it in their mouths, that this song may be a witness for me against the people of Israel.

20For when I have brought them into the land flowing with milk and honey, which I swore to give to their fathers, and they have eaten and are full and grown fat, they will turn to other gods and serve them, and despise me and break my covenant.

21And when many evils and troubles have come upon them, this song shall confront them as a witness (for it will live unforgotten in the mouths of their offspring). For I know what they are inclined to do even today, before I have brought them into the land that I swore to give."

22So Moses wrote this song the same day and taught it to the people of Israel.