Shatapatha Brahmana 1.9.2.13

1.9.2.13

athāgniṃ gṛhapatiṃ yajati | ayaṃ vā agnirloka imamevaitallokamimāḥ prajā abhiprajanayati tā imaṃ lokamimāḥ prajā abhiprajāyante tasmādagniṃ gṛhapatiṃ yajati

He then makes offering to Agni, the householder. Agni, indeed, is this world: hence it is for this world that he thereby produces offspring and that this offspring is produced: this is why he makes offering to Agni, the householder.