Shatapatha Brahmana 6.8.1.4

6.8.1.4

prajāpatireṣogniḥ | ubhayamvetatprajāpatiryacca devā yacca manuṣyāstadyadviṣṇukramavātsapre bhavato yadvavāsya daivaṃ rūpaṃ tadasya tena saṃskarotyatha yadvanīvāhyate yadevāsya mānuṣaṃ rūpaṃ tadasyatena saṃskaroti sa ha vā etaṃ sarvaṃ kṛtsnam prajāpatiṃ saṃskaroti ya evaṃ vidvānvanīvāhyate tasmādu vanīvāhyetaiva

This Agni is Pragâpati; and Pragâpati is both the gods and men. Now when the Vishnu-strides and the Vâtsapra are (performed), he thereby makes up that form of his which is divine; and when he drives him about he thereby makes up that form of his which is human. Verily, then, he who, knowing this, drives him about, makes up that whole and entire Pragâpati: let him therefore by all means drive him (Agni) about.