Catechism of the Catholic Church §2757 — excerpt
"Pray constantly" (1 Thess 5:17). It is always possible to pray. It is even a vital necessity. Prayer and Christian life are inseparable.
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.