Śatapatha Brāhmaṇa ("of a hundred paths") 3.8.1.7

3.8.1.7

tadāhuḥ | punaretadulmukaṃ haredathātrānyamevāgniṃ nirmathya tasminnenaṃ śrapayeyurāhavanīyo vā eṣa na vā eṣa tasmai yadasminnaśṛtaṃ śrapayeyustasmai vā eṣa yadasmiñcṛtaṃ juhuyuriti

As to this they say, 'Let him take back that firebrand (to the Âhavanîya); and having there (at the Sâmitra) churned out a new fire, let them cook it (the victim) thereon. For this (firebrand), surely, is âhavanîya (fit to offer upon); it is not for the purpose that they should cook uncooked (food) thereon, but for this that they should sacrifice cooked (food) thereon.'