While St. Dominic was preaching the Rosary in Carcassone, a heretic made fun of his miracles and the fifteen mysteries of the Rosary, and this prevented other heretics from being converted. As a punishment God allowed fifteen thousand devils to enter the man’s body.
His parents took him to Father Dominic to be delivered from the evil spirits. He started to pray and he begged everyone who was there to say the Rosary out loud with him, and at each Hail Mary our Lady drove a hundred devils out of the man, and they came out in the form of red-hot coals.
After he had been delivered, he abjured his former errors, was converted and joined the Rosary Confraternity. Several of his associates did the same, having been greatly moved by his punishment and by the power of the Rosary.
Source:”The Secret of the Rosary” by St.Louis de Monthfort