Śatapatha Brāhmaṇa ("of a hundred paths") 4.6.3.3

4.6.3.3

athāta stomāyanasyaiva | āgneyamagniṣṭoma ālabheta taddhi saloma yadāgneyamagniṣṭoma ālabheta yadyukthyaḥ syādaindrāgnaṃ dvitīyamālabhetaindrāgnāni hyukthāni yadi ṣoḍaśī syādaindraṃ tṛtīyamālabhetendro hi ṣoḍaśī yadyatirātraḥ syātsārasvataṃ caturthamālabheta vāgvai sarasvatī yoṣā vai vāgyoṣā rātristadyathāyathaṃ yajñakratūnvyāvartayatyetāni trīṇyayanāni teṣāṃ yatamatkāmayeta teneyāddvā upālambhyau paśū sauryaṃ dvitīyam paśumālabhate vaiṣuvate 'hanprājāpatyam mahāvrate

Then as to the manner (of animal offering) in accordance with the Stoma. At the Agnishtoma let him seize a (victim) for Agni; for it is befitting that at the Agnishtoma ('Agni's praise') he should seize a victim for Agni. If it be an Ukthya sacrifice, let him seize as the second (victim) one for Indra and Agni, for the hymns (uktha) belong to Indra and Agni. If it be a Shodasin sacrifice, let him seize as the third (victim) one for Indra; for the Shodasin (graha) is Indra. If it be an Atirâtra, let him seize as the fourth (victim) one for Sarasvatî; for Sarasvatî is Vâk (speech), and Vâk is a female, and so is râtri (fem., 'night') female. Thus he duly distinguishes between the sacrificial performances. Such are the three manners (of animal offering): he may perform in whichever manner he pleases. Two victims must needs be seized,--for Sûrya he seizes the second en the Vishuvant day, and for Pragâpati at the Mahâvrata.