Catechism of the Catholic Church §834 — excerpt
Particular Churches are fully catholic through their communion with one of them, the Church of Rome "which presides in charity." "For with this church, by reason of its pre-eminence, the whole Church, that is the faithful everywhere, must necessarily be in accord."
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. Ignatius of Antioch, Ad Rom. 1, 1: Apostolic Fathers, II/2, 192 · LG 13 · St. Irenaeus, Adv. haeres. 3, 3, 2: PG 7/1, 849 · Vatican Council I DS 3057 · St. Maximus the Confessor, Opuscula theo.: PG 91 137-140