There are a lot of different ideas related to Yoga, where it comes from, what it's all about, and the best way to observe a variety of techniques. The earliest extant systematic account of yoga and a bridge from the sooner Vedic makes use of of the term is found in the Hindu Katha Upanisad (Ku), a scripture courting from in regards to the third century BCE… It describes the hierarchy of thoughts-body constituents—the senses, mind, intellect, etc.—that comprise the foundational classes of Sāmkhya philosophy, whose metaphysical system grounds the yoga of the Yogasutras, Bhagavad Gita, and different texts and colleges (Ku3.10-11; 6.7-8).
The hymns in Ebook 2 of the Shvetashvatara Upanishad , one other late first millennium BCE text, states a process by which the physique is held in upright posture, the breath is restrained and thoughts is meditatively focussed, ideally inside a cave or a spot that is simple, plain, of silence or gently flowing water, with no noises nor harsh winds.
Translation 1 by Max Muller , The Upanishads, The Sacred Books of the East - Half 1, Oxford College Press: (He who engages in) self research, concentrates all his senses on the Self, never giving pain to any creature, besides on the tîrthas, he who behaves thus all his life, reaches the world of Brahman , and does not return, yea, he doesn't return.
Indeed, there has been some debate as as to if asceticism and its concepts of retributive action, reincarnation and spiritual liberation, may not have originated outside the orthodox vedic sphere, or even outside Aryan tradition: that a divergent historic origin would possibly account for the obvious contradiction inside 'Hinduism' between the world affirmation of the householder and the world negation of the renouncer.
The Maitrayaniya Upanishad , probably composed in a later century than Katha and Shvetashvatara Upanishads however before Patanjali's Yoga Sutra, mentions sixfold yoga technique - breath management (pranayama), introspective withdrawal of senses (pratyahara), meditation (dhyana), thoughts concentration (dharana), philosophical inquiry/inventive reasoning (tarka), and absorption/intense religious union (samadhi).