Numbers 21:5-8

And speaking against God and Moses, they said: "Why did you lead us away from Egypt, so as to die in the wilderness? Bread is lacking; there are no waters. Our soul is now nauseous over this very light food." For this reason, the Lord sent fiery serpents among the people, which wounded or killed many of them. And so they went to Moses, and they said: "We have sinned, because we have spoken against the Lord and against you. Pray, so that he may take away these serpents from us." And Moses prayed for the people. And the Lord said to him: "Make a bronze serpent, and place it as a sign. Whoever, having been struck, gazes upon it, shall live."