Śatapatha Brāhmaṇa ("of a hundred paths") 10.1.3.5

10.1.3.5

sa yaḥ sa prajāpatiḥ ayameva sa yo'yamagniścīyate'tha yā asya tāḥ pañca martyāstanva āsannetāstāḥ purīṣacitayo'tha yā amṛtā etāstā iṣṭakācitayaḥ

Now, that Pragâpati is no other than the Fire-altar which is here built up, and what five mortal parts there were of him, they are these layers of earth; and those which were immortal they are these layers of bricks.