Catechism of the Catholic Church §2147 — excerpt
Promises made to others in God's name engage the divine honor, fidelity, truthfulness, and authority. They must be respected in justice. To be unfaithful to them is to misuse God's name and in some way to make God out to be a liar.
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.