Shatapatha Brahmana 10.1.4.1

10.1.4.1

ubhayaṃ haitadagre prajāpatirāsa martyaṃ caivāmṛtaṃ ca tasya prāṇā evāmṛtā āsuḥ śarīram martyaṃ sa etena karmaṇaitayāvṛtaikadhājaramamṛtamātmānamakuruta tathaivaitadyajamāna ubhayameva bhavati martyaṃ caivāmṛtaṃ ca tasya prāṇā evāmṛtā bhavanti śarīram martyaṃ sa etena karmaṇaitayāvṛtaikadhājaramamṛtamātmānaṃ kurute

Now, at the beginning, Pragâpati was (composed of) both these, the mortal and the immortal--his vital airs alone were immortal, his body mortal: by this sacrificial performance, and by this order of proceeding, he made his body uniformly undecaying and immortal. And in like manner is the Sacrificer (composed of) both the mortal and the immortal--his vital airs alone are immortal, his body mortal: by this sacrificial performance, and by this order of proceeding, he makes his body uniformly undecaying and immortal.