Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.3.10

2.5.3.10

athāhāgnaye sviṣṭakṛte 'nubrūhīti | sa uttarasyaudanasya sarpirāsecanāttata ājyamupastṛṇīte tasya dviravadyatyathopariṣṭādājyasyābhighārayatyatikrāmatyatikramyāśrāvyāhāgniṃ sviṣṭakṛtaṃ yajeti vaṣaṭkṛte juhotyatheḍāmevāvadyati na prāśitramupahūya mārjayanta etannvekamayanam

He then says, 'Pronounce the invitatory prayer to Agni Svishtakrit!' He makes an under-layer of butter from the hollow of the northern pap, takes two cuttings from the latter, pours some butter thereon, and steps across. Having stepped across and called for the 'Sraushat,' he says, 'Pronounce the offering-prayer to Agni Svishtakrit!' and pours out the oblation as soon as the Vashat has been uttered. Thereupon he cuts off the Idâ, but no fore-portion. Having invoked (the Idâ), they cleanse themselves. This is one mode of performance.