The first psalm of Moses is not in the Book of Psalms, but in Exodus 15, where Moses leads the Israelites in the celebratory song, once they have successfully crossed the Red Sea and witnessed the drowning of the Egyptian army. It opens:
Then Moses and the Israelites sang this song to the Lord:
I will sing to the Lord, for he is highly exalted.
The horse and its rider he has hurled into the sea.
The Lord is my strength my song; and he has become by salvation.
He is my God, and I will praise him, my father’s God, and I will exalt him.