Śatapatha Brāhmaṇa ("of a hundred paths") 10.1.3.7

10.1.3.7

atha pañcamīṃ citimupadhāya purīṣaṃ nivapati tatra vakarṇīṃ ca svayamātṛṇāṃ copadadhāti hiraṇyaśakalaiḥ prokṣatyagnimabhyādadhāti sā saptamī citistadamṛtamevamasyaitābhyāmamṛtābhyāṃ tanūbhyāmetām martyāṃ tanūm parigṛhyāmṛtāmakurvanniṣṭakācitibhyām purīṣacitiṃ tato vai prajāpatiramṛto'bhavattathaivaitadyajamāna etamamṛtamātmānaṃ kṛtvā so'mṛto bhavati

And having laid down the fifth layer (of bricks), he (the Adhvaryu) scatters earth on it; thereon he lays the Vikarnî and the Svayamâtrinnâ, scatters chips of gold, and places the fire: that is the seventh layer, and that (part) is immortal; and in this way, having encompassed that mortal form of his by those two immortal forms, they made it immortal,--the layer of earth by means of two layers of bricks. Thereby, then, Pragâpati became immortal; and in like manner does the Sacrificer become immortal by making that body (of the altar) immortal.