Śatapatha Brāhmaṇa ("of a hundred paths") 2.4.4.16

2.4.4.16

atha yatpūrvedyuḥ | agnīṣomīyeṇa yajate paurṇamāsyāmabhiṣuṇotyevainametattasminnabhiṣuta etaṃ rasaṃ dadhātyetena rasena tīvrīkaroti svadayati ha vai devebhyo havyaṃ svadate hāsya devebhyo havyaṃ ya evaṃ vidvānpaurṇamāsyāṃ saṃnayati

And when, at full moon, he offers the Agni-Soma (cake) on the first day, he thereby (as it were) extracts that (Soma); and, when extracted, he adds that juice to it, and makes it strong by means of that juice. Whosoever, then, knowing this, prepares the Sânnâyya at full moon, renders his offering palatable to the gods, and his offering is palatable to the gods.