Shatapatha Brahmana 13.6.1.2

13.6.1.2

tasya trayoviṃśatirdīkṣāḥ dvādaśopasadaḥ pañca sutyāḥ sa eṣa catvāriṃśadrātraḥ sadīkṣopasatkaścatvāriṃśadakṣarā virāṭtadvirājamabhisampadyate tato virāḍajāyata virājo adhi pūruṣa ityeṣā vai sā virāḍetasyā evaitadvirājo yajñam puruṣaṃ janayati

For this (offering) there are twenty-three Dîkshâs, twelve Upasads, and five Sutyâs (Soma-days). This, then, being a forty-days’ (performance), including the Dîkshâs and Upasads, amounts to a Virâg, for the Virâg consists of forty syllables: [Vâg. S. XXXI, 5.] 'Thence Virâg (f.) was born, and from out of Virâg the Pûrusha.' This, then, is that Virâg, and from out of that Virâg he (the Sacrificer) generates the Purusha, the Sacrifice.