Augustine of Hippo
Catena Aurea · Matthäusevangelium 5
Again, ye have heard that it hath been said by them of old time, Thou shalt not forswear thyself, but shalt perform unto the Lord thine oaths: But I say unto you, Swear not at all; neither by Heaven; for it is God’s throne; Nor by the earth; for it is His footstool: neither by Jerusalem; for it is the city of the great King. Neither shalt thou swear by thy head, because thou canst not make one hair white or black. But let your communication be, Yea, yea; Nay, nay: for whatsoever is more than these cometh of evil.
(cont. Faust. xix. 23.) Inasmuch as the sin of perjury is a grievous sin, he must be further removed from it who uses no oath, than he who is ready to swear on every occasion, and the Lord would rather that we should not swear and keep close to the truth, than that swearing we should come near to perjury.