Śatapatha Brāhmaṇa ("of a hundred paths") 3.2.2.29

3.2.2.29

tadvā ṛṣīṇāmanuśrutamāsa | te yajñaṃ samabharanyathāyaṃ yajñaḥ sambhṛta evaṃ vā eṣa yajñaṃ sambharati yo dīkṣate vāgvai yajñastadyadevātra yajñasya nirdhītaṃ yadvidugdhaṃ tadevaitatpunarāpyāyayati yatparihvālaṃ vācaṃ vadati na mānuṣī prasṛtāṃ na hāpyāyayedyatprasṛtām mānuṣīṃ vācaṃ vadettasmātparihvālaṃ vācaṃ vadati na mānuṣīm prasṛtām

Now this was heard by the Rishis. They collected the sacrifice; and as that sacrifice was collected, so does he who is consecrated now collect the sacrifice (by keeping back his speech),--for the sacrifice is speech. And whatever part of the sacrifice was then sucked out and drained, that he now restores again by speaking his speech falteringly and not effusively after the manner of ordinary speech. For were he to speak effusively after the manner of ordinary speech, he would not restore (the sap of the sacrifice): therefore he speaks his speech falteringly and not effusively after the manner of ordinary speech.