Speak the Truth - Taittiriya Upanishad
Satyam eva jayate - Truth alone triumphs. (Mundaka Upanishad 3.1.6)
Asato ma sadgamaya, Tamaso ma jyotirgamaya, Mrityorma
amritam gamaya - Lead me from falsehood to truth, from darkness to light, from
death to immortality. (Brihadaranyaka Upanishad 1.3.28)
"Yato vacho nivartante aprapya manasa saha - Whence
words turn away, along with the mind, unable to reach it. (Taittiriya Upanishad
2.9.1)
Satyam vada, dharmam chara - Speak the truth, practice
righteousness. (Mahabharata)
Satyam bruhat, priyam bruhat, na bruhat satyam apriyam -
Speak the truth which is pleasant, do not speak unpleasant truth, do not speak
pleasant untruth. (Taittiriya Upanishad 1.11.1)
Yadannritam vadati, satyena patati - What is false falls
away, what is true remains. (Taittiriya Upanishad 2.8.1)