Catechism of the Catholic Church §120 — excerpt
It was by the apostolic Tradition that the Church discerned which writings are to be included in the list of the sacred books.
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: DV 8 # 3 · DS 179 · 1334-1336 · 1501-1504