Śatapatha Brāhmaṇa ("of a hundred paths") 11.2.1.1

11.2.1.1

trirha vai puruṣo jāyate etannveva mātuścādhi pituścāgre jāyate'tha yaṃ yajña upanamati sa yadyajate taddvitīyaṃ jāyate'tha yatra mriyate yatrainamagnāvabhyādadhati sa yattataḥ sambhavati tattṛtīyaṃ jāyate tasmāttriḥ puruṣo jāyata ityāhuḥ

Verily, man is born thrice, namely in this way:--first he is born from his mother and father; and when he to whom the sacrifice inclines performs offering he is born a second time; and when he dies, and they place him on the fire, and when he thereupon comes into existence again, he is born a third time;--wherefore they say, 'Man is born thrice.'