Holy Gospel of Jesus Christ according to Saint Matthew 5,33-37.
Jesus said to his disciples: "You have heard that it was said to your ancestors, 'Do not take a false oath, but make good to the Lord all that you vow.'
But I say to you, do not swear at all; not by heaven, for it is God's throne;
nor by the earth, for it is his footstool; nor by Jerusalem, for it is the city of the great King.
Do not swear by your head, for you cannot make a single hair white or black.
Let your 'Yes' mean 'Yes,' and your 'No' mean 'No.' Anything more is from the evil one."