Roman Catechism 28.8

Chapter 28 — Part III: The Decalogue — The Fifth Commandment

Section 8. Furthermore, there are on record instances of carnage executed by the special command of God. The sons of Levi, who put to death so many thousands in one day, were guilty of no sin; when the slaughter had ceased, they were addressed by Moses in these words: You have consecrated your hands this day to the Lord.