Śatapatha Brāhmaṇa ("of a hundred paths") 3.9.4.2

3.9.4.2

atha grāvāṇamādatte | te vā ete 'śmamayā grāvāṇo bhavanti devo vai somo divi hi somo vṛtro vai soma āsīttasyaitacarīraṃ yadgirayo yadaśmānastacarīreṇaivainametatsamardhayati kṛtsnaṃ karoti tasmādaśmamayā bhavanti ghnanti vā enametadyadabhiṣuṇvanti tametena ghnanti tathāta udeti tathā saṃjīvati tasmādaśmamayā grāvāṇo bhavanti

He then takes a press-stone. Now those press-stones are of rock, and Soma is a god--for Soma was in the sky, Soma was Vritra; those mountains, those rocks are his body--he thus perfects him by means of his body, makes him whole; therefore they are of rock. Moreover, in pressing him they slay him, they slay him by means of that (stone, Soma's own body); thus he rises from thence, thus he lives; therefore the press-stones are of rock.