Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.21

3.2.2.21

atha punarloṣṭaṃ nyasyati | pṛthivyā sambhavetīyaṃ vai pṛthivī devī devayajanī sā dīkṣitena nābhimihyā tasyā etadudgṛhyaiva yajñiyāṃ tanūmathāyajñiyaṃ śarīramabhyamikṣattāmevāsyāmetatpunaryajñiyāṃ tanūṃ dadhāti tasmādāha pṛthivyā sambhaveti

Thereupon he throws the clod of earth down again, with the text, 'Unite with the earth!' for truly this earth is divine, and serves as a place for the worship of the gods: it must not be defiled by him who is consecrated. Having lifted up this its sacrificially pure covering, he has relieved himself on its impure body, and now restores to it this its pure covering: therefore he says, 'Unite with the earth!'