LXX Deut 31:19

καὶ γράψατε τὰ ῥήματα τῆς ᾠδῆς ταύτης, καὶ αὐτὴν τοὺς υἱοὺς Ἰσραήλ, καὶ ἐμβαλεῖτε αὐτὴν εἰς τὸ στόμα αὐτῶν, ἵνα μοι γένηται ἡ ᾠδὴ αὕτη κατὰ πρόσωπον, μαρτυροῦσα ἐν υἱοῖς Ἰσραήλ.

Now therefore, write down for yourselves this song and teach it to the Israelites; have them recite it, so that it may be a witness for Me against them.