Kauṣītaki (Śāṅkhāyana) Brāhmaṇa 3.1.10

3.1.10

yad yajate tena uttarām /

In that he fasts on the new moon day not discerning the moon in the east, thereby he delights the first (new moon day); in that he sacrifices, thereby the second. He should fast on the second; on the second the ocean swells in accordance with the moon, its deity. The moon is the truth of the gods; therefore should he fast on the second.