Śatapatha Brāhmaṇa ("of a hundred paths") 6.7.2.11

6.7.2.11

sa yaḥ sa viṣṇuryajñaḥ saḥ | sa yaḥ sa yajño 'yameva sa yo 'yamagnirukhāyāmetameva taddevā ātmānaṃ kṛtvemāṃlokānakramanta tathaivaitadyajamāna etamevātmānaṃ kṛtvemāṃlokānkramate

Now he who is Vishnu is this sacrifice; and he who is this sacrifice is that same Agni in the ukhâ (fire-pan): into that same (Agni) the gods changed themselves, and strode through these worlds; and in like manner the Sacrificer, having changed himself into that same (Agni), strides through these worlds.