Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.20

3.2.2.20

atha yatra mekṣyanbhavati | tatkṛṣṇaviṣāṇayā loṣṭaṃ vā kiṃcidvopahantīyaṃ te yajñiyā tanūritīyaṃ vai pṛthivī devo devayajanī sā dīkṣitena nābhimihyā tasyā etadudgṛhyaiva yajñiyāṃ tanūmathāyajñiyaṃ śarīramabhimehatyapo muñcāmi na prajāmityubhayaṃ vā ata etyāpaśca retaśca sa etadapa eva muñcati na prajāmaṃhomucaḥ svāhākṛtā ityaṃhasa iva hyetā muñcanti yadudare guṣṭitam bhavati tasmā dāhāṃhomuca iti svāhākṛtām pṛthivīmāviśatetyāhutayo bhūtvā śāntāḥ pṛthivīmāviśatetyevaitadāha

When he intends to pass urine, he takes up a clod of earth or some other object by means of the deer's horn, with the text (Vâg. S. IV, 13), 'This (O Earth) is thy covering meet for worship.' For this earth truly 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 now relieves himself on its impure body, with the formula, 'I discharge not offspring, but waters,'--for so indeed he does; 'delivering from trouble, and consecrated by Svâhâ,'--for they do indeed deliver from trouble what is pressed together inside: therefore he says, 'delivering from trouble,'--'consecrated by Svâhâ, enter ye the earth!' whereby he means to say, 'Having become offerings, do ye enter the earth, appeased!'