Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.35

7.4.2.35

seyaṃ vāmabhṛt | prāṇā vai vāmaṃ yaddhi kiṃ ca prāṇīyaṃ tatsarvam bibharti teneyaṃ vāmabhṛdvāggha tveva vābhṛtprāṇā vai vāmaṃ vāci vai prāṇebhyo 'nnaṃ dhīyate tasmādvāgvāmabhṛt

This earth is the bearer of what is desirable; for--the desirable being the vital airs--this earth bears everything that breathes, and for that reason this earth is the bearer of what is desirable. But speech (the mouth) also indeed is the bearer of what is desirable; for the desirable is the vital airs, and for the (channels of) the vital airs food is put into the mouth: therefore speech is the bearer of what is desirable.