Catechism of the Catholic Church §2192 — excerpt
"Sunday . . is to be observed as the foremost holy day of obligation in the universal Church" (CIC, can. 1246 # 1). "On Sundays and other holy days of obligation the faithful are bound to participate in the Mass" (CIC, can.
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.