"Again you have heard that it was said to those of old, "You shall not swear falsely, but shall perform your oaths to the Lord.'
Matthew 5:33
Surrounding context
5:32 But I say to you that whoever divorces his wife for any reason except sexual immorality causes her to commit adultery; and whoever marries a woman who is divorced commits adultery.
5:33 "Again you have heard that it was said to those of old, "You shall not swear falsely, but shall perform your oaths to the Lord.'
5:34 But I say to you, do not swear at all: neither by heaven, for it is God's throne;