Here is the earliest reference to yoga, a mantra revealed to Rishi Shyavashva Atreya.

युञ्जते मन उत युञ्जते धियो विप्रा विप्रस्य बृहतो विपश्चित:
वि होत्रा दधे वयुनाविदेक इन्मही देवस्य सवितु: परिष्टुति: — Rgveda 5.81.1

Yuñjate mana uta yuñjate dhiyo viprā viprasya bṛhato vipaścitaḥ
Vi hotrā dadhe vayunāvideka inmahī devasya savituḥ pariṣṭutiḥ

yunjate mana uta yunjate dhiyo viprA viprasya bRRihato vipashcitaH
vi hotrA dadhe vayunAvideka inmahI devasya savituH pariSTutiH

They yoke the mind in yoga
They yoke the intelligence in yoga;
They the great wise ones who belong
To the expansive wisest One.

There is but one Master of Wisdom
Who upholds all our sacred endeavours.
Indeed great is the all round praise
to that celestial divine sun-like Brilliant One.

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