NASB
""Now therefore, write this song for yourselves, and teach it to the sons of Israel; put it on their lips, so that this song may be a witness for Me against the sons of Israel."
— Deuteronomy 31:19, NASB
The LORD said to Moses, "Behold, you are about to lie down with your fathers; and this people will arise and play the harlot with the strange gods of the land, into the midst of which they are going, and will forsake Me and break My covenant which I have made with them.
"Then My anger will be kindled against them in that day, and I will forsake them and hide My face from them, and they will be consumed, and many evils and troubles will come upon them; so that they will say in that day, 'Is it not because our God is not among us that these evils have come upon us?'
"But I will surely hide My face in that day because of all the evil which they will do, for they will turn to other gods.
"Now therefore, write this song for yourselves, and teach it to the sons of Israel; put it on their lips, so that this song may be a witness for Me against the sons of Israel.
"For when I bring them into the land flowing with milk and honey, which I swore to their fathers, and they have eaten and are satisfied and become prosperous, then they will turn to other gods and serve them, and spurn Me and break My covenant.
"Then it shall come about, when many evils and troubles have come upon them, that this song will testify before them as a witness (for it shall not be forgotten from the lips of their descendants); for I know their intent which they are developing today, before I have brought them into the land which I swore."
So Moses wrote this song the same day, and taught it to the sons of Israel.