Shatapatha Brahmana 7.5.1.21

7.5.1.21

tadeṣa śloko 'bhyuktaḥ | tadvai sa prāṇo 'bhavaditi taddhi sa prāṇo 'bhavanmahā bhūtvā prajāpatiriti mahānhi sa tadabhavadyadenamete devāḥ prāpadyanta bhujo bhujiṣyā vittveti prāṇā vai bhujo 'nnam bhujiṣyā etatsarvaṃ vittvetye tadyatprāṇānprāṇayatpurītyātmā vai pūryadvai prāṇānprāṇayattasmātprāṇā devā atha yatprajāpatiḥ prāṇayattasmādu prajāpatiḥ prāṇo yo vai sa prāṇa eṣā sā gāyatryatha yattadannameṣa sa viṣṇurdevatātha yā so 'rgeṣa sa udumbaraḥ

It is thereto that this verse applies,--'Then, indeed, he became that breath,'--for that breath he then indeed became;--'having become the great Pragâpati,'--for great he indeed then became, when those gods entered him;--'having obtained the benefits, the beneficial,'--the benefits doubtless are the vital airs (breaths), and the beneficial are the food: thus, having obtained all that;--'when he breathed the breaths in the stronghold;'--the stronghold doubtless is the self (body), and inasmuch as he breathed the breaths, the gods are the breaths; and inasmuch as Pragâpati breathed, the breath also is Pragâpati; and verily he who is that breath, he is that Gâyatrî;--and as to that food, that is Vishnu, the deity; and as to that strength, that is the Udumbara (tree).