Shatapatha Brahmana 10.3.5.2

10.3.5.2

ayamevākāśo jūḥ yadidamantarikṣametaṃ hyākāśamanu javate tadetadyajurvāyuścāntarikṣaṃ ca yacca jūśca tasmādyajureṣa eva yadeṣa hyeti tadetadyajurṛkṣāmayoḥ pratiṣṭhitamṛkṣāme vahatastasmātsamānairevādhvayurgrahaiḥ karma karotyanyānyanyāni stutaśastrāṇi bhavanti yathā pūrvābhyāṃ syanttvāparābhyāṃ dhāvayettādṛktat

And the course (gûh) is this space, to wit, this air, for along this space it (the wind) courses; and the Yagus is both the wind and the air--the 'yat' and the 'gûh'--whence (the name) Yagus. And the 'yat' (that which goes) is this (Adhvaiyu), for when he 'goes' on (performing), the Rik and Sâman carry that Yagus established on the Rik and Sâman. Hence the Adhvaryu performs his work with the very same Grahas (cups of Soma), (while) there are each time different stotras (chants) and sastras (recitations): it is just as if, after driving with a first pair (of horses), one drives with a second pair.