Shatapatha Brahmana 6.5.1.1

6.5.1.1

parṇakaṣāyaniṣpakvā etā āpo bhavanti | sthemne nveva yadveva parṇakaṣāyeṇa somo vai parṇaścandramā u vai soma etadu vā ekamagnirūpametasyaivāgnirūpasyopāptyai

That water (used for working the clay) has been boiled by means of resin of the palâsa tree (butea frondosa), just for the sake of firmness. And as to why (it is done) by palâsa resin;--the palâsa tree doubtless is Soma, and Soma is the moon, and that (moon) indeed is one of Agni's forms: it is for the obtainment of that form of Agni (that palâsa resin is used).