Chapter 25 — Part III: The Decalogue — The Second Commandment
Section 42. Unjust Oaths — This Commandment is also violated, if justice, which is one of the three conditions of an oath, be wanting. Hence he who swears to commit a mortal sin, for example, to perpetrate murder, violates this Commandment, even though he speak seriously and from his heart, and his oath possess what we before pointed out as the first condition of every oath, that is, truth.