The devil trembles and flees when he hears this prayer

One day, after Saint Bernard had prayed a Hail Mary with great respect in front of a statue of the Virgin, the statue gently bowed her head and answered: "I salute you, Bernard!"

Blessed Alan said that at this prayer Heaven rejoices and the devil trembles and runs away. Saint Thomas in Kempis asserts, from personal experience, that the demon flees when he hears it.

Saint Alphonsus Liguori had a great devotion to the Hail Mary. He recited it every day on the hour every hour. When the hour struck, he would stop to recite it, whatever his occupation and the people around him. When someone expressed some surprise at this habit of his, he replied, "An Ave Maria is a treasure that surpasses the price of the whole world."

The Children's Rosary

From the booklet Histoires sur la Sainte Vierge IX, p. 4-5