Śatapatha Brāhmaṇa ("of a hundred paths") 2.5.3.13

2.5.3.13

athāha somāyānubrūhīti | saumyamājyabhāgaṃ sa sthālyā eva caturājyasyāvadāyātikrāmatyatikramyāśrāvyāha somaṃ yajeti vaṣaṭkṛte juhoti

He then says, 'Pronounce the invitatory prayer to Soma!' with a view to Soma's butter-portion. He then takes four cuttings of butter from the pot, and steps across. Having stepped across, and called for the Sraushat, he says, 'Pronounce the offering-formula to Soma!' and pours out the oblation, as soon as the Vashat has been uttered.