Translated in Aldous Huxley's novel, Island, as "thou art That"; the heart of the philosophy held by the Mahayana Buddhists of Pala.

"Tat tvam asi," he repeated. "It looks like a proposition in metaphysics; but what it actually refers to is psychological experience, and the operations by means of which the experience can be lived through are described by our philosophers, so that anyone who's willing to perform the necessary operations can test the validity of Tat tvam asi for himself. The operations are called yoga, or dhyana, or Zen -- or, in certain circumstances, maithuna."

-- Island, by Aldous Huxley