Upanishads[edit]
Alexander Wynne, author of The Origin of Buddhist Meditation, observes that formless meditation and elemental meditation might have originated in the Upanishadic tradition.[103] The earliest reference to meditation is in the Brihadaranyaka Upanishad, one of the oldest Upanishads.[83] Chandogya Upanishad describes the five kinds of vital energies (prana). Concepts used later in many yoga traditions such as internal sound and veins (nadis) are also described in the Upanishad.[69] Taittiriya Upanishad defines yoga as the mastery of body and senses.[104]
The term "yoga" first appears in the Hindu scripture Katha Upanishad (a primary Upanishad c. 400 BCE) where it is defined as the steady control of the senses, which along with cessation of mental activity, leads to the supreme state.[83][note 13] Katha Upanishad integrates the monism of early Upanishads with concepts of samkhya and yoga. It defines various levels of existence according to their proximity to the innermost being Ātman. Yoga is therefore seen as a process of interiorization or ascent of consciousness.[106][107] It is the earliest literary work that highlights the fundamentals of yoga. Shvetashvatara Upanishad (c. 400-200 BCE) elaborates on the relationship between thought and breath, control of mind, and the benefits of yoga.[107] Like the Katha Upanishad the transcendent Self is seen as the goal of yoga. This text also recommends meditation on Om as a path to liberation.[108] Maitrayaniya Upanishad (c. 300 BCE) formalizes the sixfold form of yoga.[107] Physiological theories of later yoga make an appearance in this text.[109][110]
While breath channels (nāḍis) of yogic practices had already been discussed in the classical Upanishads, it was not until the eighth-century Buddhist Hevajra Tantra and Caryāgiti, that hierarchies of chakras were introduced.[111][112] Further systematization of yoga is continued in the Yoga Upanishads of the Atharvaveda (viz., Śāṇḍilya, Pāśupata, Mahāvākya)[clarification needed].[113]