Śatapatha Brāhmaṇa ("of a hundred paths") 7.5.2.21

7.5.2.21

atha dakṣiṇato 'jam | yo agniragneradhyajāyatetyagnirvā eṣo 'gneradhyajāyata śokātpṛthivyā u ta vā divasparīti yadvai prajāpateḥ śokādajāyata taddivaśca pṛthivyai ca śokādajāyata yena prajā viśvakarmā jajāneti vāgvā ajo vāco vai prajā viśvakarmā jajāna tamagne heḍaḥ pari te vṛṇaktviti yathaiva yajustathā bandhuḥ

Then on the right side (he puts the head of) the he-goat, with (Vâg. S. XII I, 45), 'The Agni who was born from Agni,' for that Agni was indeed born from Agni;--'from the pain of the earth or also of the sky;' for what was born from the pain (or heat) of Pragâpati, that was born from the pain of the sky and the earth;--'whereby Visvakarman begat living beings,'--the he-goat (or, the unborn one) is Vâk (Speech), and from Vâk Visvakarman begat living beings;--'him, O Agni, may thy wrath spare!' as the text, so the meaning.