Śatapatha Brāhmaṇa ("of a hundred paths") 1.7.2.13

1.7.2.13

devapātraṃ vā eṣa yadvaṣaṭkāraḥ | tadyathā pātra uddhṛtya prayacedevaṃ tadatha yatpurā vaṣaṭkārājjuhuyādyathādho bhūmau nidigdhaṃ tadamuyā syādevaṃ tattasmādu saha vaiva vaṣaṭkāreṇa juhuyādvaṣaṭkṛte vā

A vessel of the gods, doubtless, is that vashat. Even as, after ladling, one would mete out (food) into a vessel, so here. If, on the other hand, he were to make the offering before the vashat, it would be lost, as would be that (food) falling to the ground: for this reason also let him make the offering either simultaneously with the vashat or after it has been pronounced.