Śatapatha Brāhmaṇa ("of a hundred paths") 4.2.5.14

4.2.5.14

tasmādāgneyamagniṣṭoma ālabhate | taddhi saloma yadāgneyamagniṣṭoma ālabheta yadyukthyaḥ syādaindrāgnaṃ dvitīyamālabhetaindrāgnāni hyukthāni yadi ṣoḍaśī syādaindraṃ tṛtīyamālabhetendro hi ṣoḍaśī yadyatīrātraḥ syātsārasvataṃ caturthamālabheta vāgvai sarasvatī yoṣā vai vāgyoṣā rātristadyathāyathaṃ yajñakratūnvyāvartayati

Let him therefore, at the Agnishtoma, slay a (victim) sacred to Agni, for there is harmony when, at the Agnishtoma, he slays a (victim) for Agni. If it be an Ukthya sacrifice, let him slay one to Indra and Agni in the second place, for songs of praise (uktha) refer to Indra and Agni. If it be a Shodasin sacrifice, let him slay one to Indra in the third place, for the sixteenfold chant (shodasin) means Indra. If it be an Atirâtra, let him slay one to Sarasvatî in the fourth place, for Sarasvatî is speech, and speech (vâk, fem.) is female, as the night (râtri, fem.) is female: he thus duly distinguishes the forms of sacrifice.