21 Feeling certain that Our sons throughout the world will respond willingly and generously to this Our invitation, We impart, from the fullness of Our heart and as an evidence of Our favor and an augury of heavenly graces, to each and every one of you, to the flock entrusted to each of you and particularly to those who, especially during the month of October, will devoutly recite the holy Rosary according to Our intentions, Our Apostolic Blessing. Given in Rome, at St. Peter's, the 15th day of September, the Feast of the Seven Sorrows of the Virgin Mary, in the Year 1951, the 13th of Our pontificate.
Source: Ingruentium Malorum (Vatican.va)