Śatapatha Brāhmaṇa ("of a hundred paths") 4.3.2.12

4.3.2.12

yatra dyāvāpṛthivyaṃ śasyate | ime ha vai dyāvāpṛthivī imāḥ prajā upajīvanti tadanayorevaitaddyāvāpṛthivyo rasaṃ dadhāti te rasavatyā upajīvanīye imāḥ prajā upajīvanti sa vā omityeva pratigṛṇīyāttaddhi satyaṃ taddevā viduḥ

When (the hymn) to Heaven and Earth is recited. Now these creatures subsist on those two, the heaven and the earth--he thereby imbues those two, heaven and earth, with vigour; and upon those two, thus vigorous and affording the means of subsistence, these creatures subsist. Let him respond with 'Om!' only, for that is truth, that the gods know.