"Thus have I heard" is a standard formula for the beginning of Buddhist Suttas (Pali).........or Sutras (Sanskrit) Thus have I heard. Pali = Evam me sutta, Sanskrit = Evam maya srutam Theravada Texts, the Southern School, would be in Pali. Mayayana Texts, the Northern School, would be in Sanskrit. Theravada does have an Authorised Canon. Mahayana, not so*, yet many Mahayana Sutras have become established "favorites" and gathered many commentaries. The phrase, "Thus have I heard" is often understood, particularly in the Theravada, as a "seal of authenticity", that what is being then recited are the recorded words of the Buddha himself. The phrase gathers much over time. Given that it is seen as establishing authentic words of the Buddha, the fact that his honorific title is Tathagata is significant in this context. Tathagata, or "he who has thus come" and more, one actually beyond all coming and going. Thus, the words of the text actually take on a deep significance for many Buddhists. This should be considered and reflected upon. Again, the Dharma itself is described as ehipassiko, or "a come and see (for oneself)" sort of thing. Again significant. It is authenticated in practice, in living the Path. Its authentication, ultimately, does not derive from "faith" in its truth as such, nor in any scholarly analysis that seeks authentication by tracing back the genesis of the text via historical documents, word of mouth, or other such means. So, "Thus have I heard" * I believe that there are in fact Chinese and Tibetan Canons.