Shatapatha Brahmana 7.5.1.12

7.5.1.12

atholūkhalamusale upadadhāti | viṣṇurakāmayatānnādaḥ syāmiti sa ete iṣṭake apaśyadulūkhalamusale te upādhatta te upadhāyānnādo 'bhavattathaivaitadyajamāno yadulūkhalamusale upadadhāti yena rūpeṇa yatkarma kṛtvā viṣṇurannādo 'bhavattena rūpeṇa tatkarma kṛtvānnādo 'sānīti tadetatsarvamannaṃ yadulūkhalamusale ulūkhalamusalābhyāṃ hyevānnaṃ kriyata ulūkhalamusalābhyāmadyate

He then puts down a mortar and pestle. Vishnu desired, 'May I be an eater of food!' He saw these two bricks, the mortar and pestle. He placed them on (the altar); and by placing them thereon, he became an eater of food. In like manner, when the Sacrificer now places a mortar and pestle thereon, (he does so) thinking, 'I want to be an eater of food by the same means (rûpa), by performing the same rite by which Vishnu became an eater of food.' Now the mortar and pestle mean all (kinds of) food; for by the mortar and pestle food is prepared, and by means of them it is eaten.