Catechism of the Catholic Church §1285 — excerpt
Baptism, the Eucharist, and the sacrament of Confirmation together constitute the "sacraments of Christian initiation," whose unity must be safeguarded. It must be explained to the faithful that the reception of the sacrament of Confirmation is necessary for the completion of baptismal grace.
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: Roman Ritual, Rite of Confirmation (OC), Introduction 1 · LG 11 · OC, Introduction 2