Matthew 5:33-37 (New International Version)
Oaths
33“Again, you have heard that it was said to the people long ago, ‘Do not break your oath, but keep the oaths you have made to the Lord.’ 34But I tell you, Do not swear at all: either by heaven, for it is God’s throne; 35or by the earth, for it is his footstool; or by Jerusalem, for it is the city of the Great King. 36And do not swear by your head, for you cannot make even one hair white or black. 37Simply let your ‘Yes’ be ‘Yes,’ and your ‘No,’ ‘No’; anything beyond this comes from the evil one.