Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 26.2.4

26.2.4

ya eva eṣa pṛṣṭhyaḥ ṣaḍahaḥ punaḥ parastāt paryeti tena māsā āvṛttā iti vadantaḥ / (soma: chandomāh)

saying: “By this very Pṛṣṭhya six-day period that comes around again beyond, the months are turned round.”