אָז יָשִׁיר מֹשֶׁה וּבְנֵי יִשְׂרָאֵל אֶת הַשִּׁירָה הַזֹּאת לַה׳ וַיֹּאמְרוּ לֵאמֹר
Az yashir Moshe uv'nei Yisrael et hashirah hazot l'Adonai vayom'ru leimor
Then Moses and the Children of Israel sang this song to the Lord, and they said:
אָז יָשִׁיר = "Then he WILL sing" — future tense. The Sages see this as a hint to the future resurrection.