Catechism of the Catholic Church §2001 — excerpt
The preparation of man for the reception of grace is already a work of grace. This latter is needed to arouse and sustain our collaboration in justification through faith, and in sanctification through charity.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.
Also cites: St. Augustine, De gratia · libero arbitrio, 17: PL 44, 901 · St. Augustine, De natura · gratia, 31: PL 44, 264