Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.3.29

3.9.3.29

ta āyanti | pratyupatiṣṭhate 'gnīccātvāle vasatīvarībhiśca hotṛcamasena ca sa uparyupari cātvālaṃ saṃsparśayati vasatīvarīśca maitrāvaruṇacamasaṃ ca samāpo adbhiragmata samoṣadhībhiroṣadhīriti yaścāsau pūrvedyurāhṛto yajñasya raso yaścādyāhṛtastamevaitadubhayaṃ saṃsṛjati

They come back. The Agnîdh takes up his position opposite to the pit with the Vasatîvarî water and the Hotri's cup. Close over the pit he (the Adhvaryu) makes the Vasatîvarî water and the Maitrâvaruna's cup touch one another, with, 'Water hath united with water, plants with plants!' the sap of the sacrifice which was fetched yesterday and that fetched to-day, both kinds he thereby mixes together.