Śatapatha Brāhmaṇa ("of a hundred paths") 7.4.2.37

7.4.2.37

yadvapasyāḥ pañca purastādupadadhāti | annaṃ vā āpo 'napihitā vā annena prāṇāstāmanantarhitāmṛtavyābhyāmupadadhātyṛtuṣu tadvācam pratiṣṭhāpayati seyaṃ vāgṛtuṣu pratiṣṭhitā vadati

And as to why he lays down in front five Apasyâs,--water (ap) is food, and by food (the organs of) the vital airs are not closed up. He lays down (the Ashâdhâ) close to the two seasonal ones: he thereby establishes speech in the seasons, and hence speech (the mouth) speaks here, firmly established in the seasons.