Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.1.1

7.4.1.1

ātmannagniṃ gṛhṇīte ceṣyan | ātmano vā etamadhijanayati yādṛśādva jāyate tādṛṅṅeva bhavati sa yadātmannagṛhītvāgniṃ cinuyānmanuṣyādeva manuṣyaṃ janayenmartyānmartyamanapahatapāpmano 'napahatapāpmānamatha yadātmannagniṃ gṛhītvā cinoti tadagnerevādhyagniṃ janayatyamṛtādamṛtamapahatapāpmano 'pahatapāpmānam

Being about to build Agni (the fire-altar), he takes him up into his own self; for from out of his own self he causes him to be born, and wherefrom one is born, suchlike he becomes. Now were he to build up Agni without taking him up into his own self, he would beget man from man, mortal from mortal, one not freed from sin from one not freed from sin; but when he builds up Agni after taking him up into his own self, he causes Agni to be born from Agni, the immortal from the immortal, the sinless from the sinless.