Deuteronomy 31:19, 21, 26

Now therefore write ye this song for you, and teach 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 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 go about, even now, before I have brought them into the land which I sware.

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