Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 26.2.18

26.2.18

anvābhiplavikāḥ stomā āvartatnte daśarātram anupṛṣṭhyas stomā iti vadantaḥ /

perform the Go and Āyus as inverted; the Go and Āyus are day and night; day and night are inverted towards each other; moreover the Go and Āyus are sky and earth; sky and earth are inverted towards each other; moreover the Go and Āyus are expiration and inspiration; expiration and inspiration, being inverted, find support in each other. Some perform them in the forward order, saying 'The Go and Āyus should be performed in the forward direction; the Abhiplava Stomas are reversed, and the Pṛṣṭhya Stomas in the ten-night (period).' They say 'The Go and Āyus are the second and the third day.'