The St. Michael Prayer
St. Michael the Archangel, defend us in battle, be our protection against the wickedness and snares of the devil. May God rebuke him we humbly pray; and do thou, O Prince of the Heavenly host, by the power of God, cast into hell Satan and all the evil spirits who prowl about the world seeking the ruin of souls.
St. Michael in Scripture
And there was a great battle in heaven, Michael and his angels fought with the dragon, and the dragon fought and his angels:  And they prevailed not, neither was their place found any more in heaven.  And that great dragon was cast out, that old serpent, who is called the devil and Satan, who seduceth the whole world; and he was cast unto the earth, and his angels were thrown down with him. - Rev 12:7-8
But at that time shall Michael rise up, the great prince, who standeth for the children of thy people: and a time shall come such as never was from the time that nations began even until that time. And at that time shall thy people be saved, every one that shall be found written in the book. - Dan 12:1