Śatapatha Brāhmaṇa ("of a hundred paths") 6.2.2.27

6.2.2.27

yadvevāmāvāsyāyām | reto vā etadbhūtamātmānaṃ siñcatyukhāyāṃ yonau yaddīkṣate tasmā etam purastāllokaṃ karoti yaddīkṣito bhavati taṃ kṛtaṃ lokamabhi jāyate tasmādāhuḥ kṛta lokam puruṣo 'bhi jāyata iti

And, again, why he (does so) at new moon;--when he performs the initiation, he verily pours out his 'own self, as seed, into the fire-pan, the womb; and when he becomes initiated, he makes for it (his self) that world (or place) beforehand, and he is born into the world made by him: hence they say, Man is born into the world made (by him).'