The oldest evidence was found in India, coming up in some of the earliest known Hindu Sanskrit texts, known as Upanishads. For example, the Brihadaranyaka Upanishad and the Chandogya Upanishad, both place importance on the unity of the soul is a concept known as Atman. Also, the idea of nondualism is associated with some of the teachings of the Buddha, particularly with the so-called two truths doctrine.