This prayer to Saint Michael the Archangel, originally composed in Latin, was written by Pope Leo XIII in 1886. Between then and 1965, it was recited after every Low Mass at Pope Leo's order.
In recent years, a number of parishes have begun reciting the prayer once more, and many individual Catholics have kept the practice up. Both Pope John Paul II and Pope Benedict XVI have urged the faithful to pray it daily, and especially after Mass.
Prayer to Saint Michael the Archangel
Saint 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 evil spirits who wander through the world seeking the ruin of souls. Amen.