Deuteronomy 31:19, 21, 26

Now therefore write ye this song for you, and teach thou it the children of Israel: put it in their mouths, that this song may be a witness for me against the children of Israel.

And it shall come to pass, when many evils and troubles are come upon them, that this song shall testify before 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 this day, before I have brought them into the land which I sware.

Take this book of the law, and put it by the side of the ark of the covenant of Jehovah your God, that it may be there for a witness against thee.