CCC 2164
Life in Christ›SECTION TWO THE TEN COMMANDMENTS›CHAPTER ONE YOU SHALL LOVE THE LORD YOUR GOD WITH ALL YOUR HEART, AND WITH ALL YOUR SOUL, AND WITH ALL YOUR MIND›IN BRIEF
"Do not swear whether by the Creator, or any creature, except truthfully, of necessity, and with reverence" (St. Ignatius of Loyola, Spiritual Exercises, 38).