Śatapatha Brāhmaṇa ("of a hundred paths") 3.5.4.24

3.5.4.24

atha grāvṇa upāvaharati | dantā haivāsya grāvāṇastadyadgrāvabhirabhiṣuṇvanti yathā dadbhiḥ psāyādevaṃ tattānnidadhāti vaiṣṇavā stheti vaiṣṇavā hyeta etadu yajñasya śiraḥ saṃskṛtam

He then brings down the (five) press-stones. The press-stones, doubtless, are his (Vishnu's) teeth: hence, when they press (the Soma) with the stones it is as if he chewed with his teeth. He puts them down with, 'Ye are Vishnu's own;' for they indeed belong to Vishnu. Thus, then, the head of the sacrifice is complete.