Aitareyabrahmana 3.32

3.32

āgneyī prathamā ghṛtayājyā, saumī saumyayājyā, vaiṣṇavī ghṛtayājyā.
tvaṃ soma pitṛbhiḥ saṃvidāna iti saumyasya pitṛmatyā yajati
ghnauti vā etat somaṃ yad abhiṣuṇvanti,
tasyaitām anustaraṇīṃ kurvanti yat saumyaḥ.
pitṛbhyo vā anustaraṇī, tasmāt saumyasya pitṛmatyā yajaty
avadhiṣur vā etat somaṃ yad abhyasuṣavus, tad enam punaḥ sambhāvayanti
punar āpyāyayanty upasadāṃ rūpeṇopasadāṃ kila vai tad rūpaṃ yad etā devatā:
Agniḥ Somo Viṣṇur iti
pratigṛhya saumyaṃ hotā pūrvaś chandogebhyo 'vekṣeta
taṃ haike pūrvaṃ chandogebhyo haranti. tat tathā na kuryād.
vaṣaṭkartā prathamaḥ sarvabhakṣān bhakṣayatīti ha smāha,
tenaiva rūpeṇa tasmād vaṣaṭkartaiva pūrvo
'vekṣetāthainaṃ chandogebhyo haranti

iii. 32 (xiii. 8). The first offering verse for the ghee is addressed to Agni,

the offering verse for (the pap for) Soma is addressed to Soma, the offering verse for the ghee is addressed to Viṣṇu. For (the pap for) Soma he uses as offering verse ‘Thou, O Soma, in unison with the fathers,’ which contains (the word) ‘fathers’. They slay the Soma in that they press it; for it they perform (the offering of) a barren cow in the form of (the pap) for Soma; the barren cow is for the fathers; therefore (a verse) containing (the word) ‘fathers’ he uses as offering verse for (the pap for) Soma. They have killed Soma in that they pressed it; thus do they again bring it into being; they swell it up again with the symbol of the Upasads, these deities, Agni, Soma, and Viṣṇu are the symbol of the Upasads. Having taken (the pap) for Soma before the Sāman singers the Hotṛ should look into it; some indeed give it first to the Sāman singers, but that he should not do. ‘The sayer of vaṣaṭ eats first all foods’, he used to say; in this way therefore the sayer of vaṣaṭ should first look into it, then they give it to the Sāman singers.