Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.2.32

2.5.2.32

athādhvaryurevāha somāyānubrūhīti | saumyamājyabhāgaṃ tā ubhāveva caturājyasyāvadāyātikrāmato 'tikramyāśrāvyādhvaryurevāha somaṃ yajeti tā ubhāveva vaṣaṭkṛte juhutaḥ

The Adhvaryu then says, 'Pronounce (the invitatory prayer) to Soma!' referring to Soma's butter-portion. Both having taken four cuttings of butter, they step across. Having stepped across and called for the 'Sraushat,' the Adhvaryu says (to the Hotri), 'Pronounce the offering-prayer to Soma!' After the 'Vashat' has been uttered, they both pour out the oblation.