Śatapatha Brāhmaṇa ("of a hundred paths") 4.4.5.15

4.4.5.15

atha vāruṇa ekakapālaḥ puroḍāśo bhavati | yo vā asya raso 'bhūdāhutibhyo vā asya tamajījanadathaitacarīraṃ tasminna raso 'sti raso vai puroḍāśastadasminnetaṃ rasaṃ dadhāti tadenametena rasena saṃgamayati tadenamato janayati sa enaṃ jāta eva sañjanayati tasmādvāruṇa ekakapālaḥ puroḍāśo bhavati

Then follows a cake on one potsherd for Varuna. For whatever sap there had been in him (Soma), that sap of his he has produced (extracted) for the offerings. Now that body: there is no sap in it. But the cake is sap: that sap he puts into it. Thus he unites him with that sap, and so produces him from it,--he (Soma), even when produced, produces him (the sacrificer): hence there is a cake on -one potsherd for Varuna.