Oh my God! for Thy greater glory, and to imitate as closely as possible the generous Heart of Jesus, my Redeemer, and also to testify my devotion to the Blessed Virgin, my Mother, who is also the Mother of the Souls in Purgatory, I place in her hands all my satisfactory works, as well as the fruit of all those which may be offered for my intention after my death, that she may apply them to the Souls in Purgatory according to her wisdom and good pleasure. Amen.
This act is approved and encouraged by Pope Benedict XIII (1724-1730).
More details: Catholic Tradition