Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.2.2

3.9.2.2

sa yadvasatīvarīracaiti | tamevaitadrasamāhṛtya yajñe dadhāti rasavantaṃ yajñaṃ karoti tasmādvasatīvarīracaiti

And when he goes for the Vasatîvarî water, he fetches that same sap and puts it into the sacrifice, and makes the sacrifice sapful; this is why he goes for the Vasatîvarî water.