Don't swear by heaven
Matthew 5:34 But I tell you this: do not ever swear an oath. What is an oath? You cannot say, “I swear by heaven”—for heaven is not yours to swear by; it is God’s throne.
Don't swear by earth
Matthew 5:35 And you cannot say, “I swear by this good earth,” for the earth is not yours to swear by; it is God’s footstool. And you cannot say, “I swear by the holy city Jerusalem,” for it is not yours to swear by; it is the city of God, the capital of the King of kings.
Don't swear by your own head
Matthew 5:36 You cannot even say that you swear by your own head, for God has dominion over your hands, your lips, your head. It is He who determines if your hair be straight or curly, white or black; it is He who rules over even this small scrap of creation.
Instead of swearing, keep your word!
Matthew 5:37 You need not swear an oath—any impulse to do so is of evil. Simply let your “yes” be “yes,” and let your “no” be “no.”