Shatapatha Brahmana 6.5.3.4

6.5.3.4

athādhyātmam | ātmaivokhā vāgaṣāḍhā tām pūrvā karoti purastāddhīyamātmano vāktāmetasyā eva mṛdaḥ karotyātmano hyeveyaṃ vāṅnahiṣi karoti mahiṣī hi vāktryālikhitā bhavati tredhāvihitā hi vāgṛco yajūṃṣi sāmānyatho yadidaṃ trayaṃ vāco rūpamupāṃśu vyantarāmuccaiḥ

Now as regards the self (or body): the fire-pan, indeed, is the self (of Agni). The 'invincible' (brick) is speech: that she (the wife) makes first, for this speech is foremost in the body. She makes it from that same clay, for this speech is of the body. The (Sacrificer's) consecrated consort makes it, for speech is a 'mahishî.' It is marked with three lines, for speech is divided into three kinds, Rik-verses, Yagus-formulas, and Sâman-tunes; and because of this threefold form of speech, low-voiced, half-loud, and loud.