Catechism of the Catholic Church §812 — excerpt
Only faith can recognize that the Church possesses these properties from her divine source. But their historical manifestations are signs that also speak clearly to human reason.
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: Vatican Council I, DS Filius 3: DS 3013