Longer Catechism (Orthodox) 26.534

Chapter 26 — Part III — The Ten Commandments

Section 534. Q. Are not such oaths specially forbidden in holy Scripture? A. The Saviour says: I say unto you, Swear not at all, but let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil. Matt. v. 34, 37.