Śatapatha Brāhmaṇa ("of a hundred paths") 3.3.1.3

3.3.1.3

atha saptamam padam paryupaviśanti | sa hiraṇyam pade nidhāya juhoti na vā anagnāvāhutirhūyate 'gniretasaṃ vai hiraṇyaṃ tatho hāsyaiṣāgnimatyevāhutirhutā bhavati vajro vā ājyaṃ vajreṇaivaitadājyena spṛṇute tāṃ spṛtvā svīkurute

They now sit down round the seventh footprint; and having laid down the piece of gold in the foot-print, he offers. For offering is made on nothing but fire, and the gold has sprung from Agni's seed: and thus that offering of his is indeed made over the fire. And the clarified butter being a thunderbolt, he now delivers her (the cow) by means of that thunderbolt, the butter; and by delivering her he makes her his own.