Let your conduct be marked by Truthfulness in Word, Deed and Thoughtfulness in Word, Deed and Thought.
Taittiriya Upanishad 1.11.1
May the truth-spoken word triumph over the false-spoken word which destroys the holy-order.
Tzu-chang asked about getting on with people. The master mind said, “Be loyal and true with every word, serious and careful in all you do, and you will get on well enough even though you find yourself among barbarians But if you are disloyal and untrustworthy in your speech, frivolous and careless in your acts, event though you are among your own neighbours, how can you hope to get on well?”
Fulfil the covenant of God once you have pledged it, and do not break any oaths once they have been sworn to. You have set up God as a guarantee for yourself; God knows everything you are doing. Do not be like a woman who unravels her yarn after its strand and firmly spun. Nor take any oaths in order to snatch an advantages over one another, to make one party more numerous than the other, for God will test you by this.
You have heard that it was said to the men of old, “You shall not swear falsely, but shall perform to the Lord what you have sworn.” But I say to you, do not swear at all, either by heaven, for it the throne of God… And do not swear by your head, for you cannot make one hair white or black. Let what you say be simply “yes” or “no”; nothing more than this comes from evil.