Shatapatha Brahmana 11.1.4

Now, some people enter upon the fast when they (still) see (the moon, on the fourteenth day of the half-month), thinking, 'To-morrow he will not rise,'--either on account of clouds or not having ascertained properly, they enter upon the fast, and (in the morning) he rises over him. Now if he (the moon) should rise on (the material for) the oblation being not yet taken out, then that approved (procedure is followed) and the same fasting-observance. The sour curds from last night's milking they use for coagulating the sacrificial food; they let the calves join (their mothers), and drive them away again.

In the afternoon he drives them away with the parna-branch; and as there that approved oblation of the New-moon offering (is prepared) so here. But if he should not care to undergo (again) the fasting-observance, or if (the moon) were to rise over (the material for) the oblation already taken out, then let him do otherwise: having properly cleansed the rice-grains of the husks, he cooks the smaller ones as a cake on eight potsherds for Agni Dâtri (the Giver).

And the sour curds (from the milk) milked on the day before (he prepares) for Indra Pradâtri (the Bestower); and those (larger) rice-grains he cooks in boiled fresh milk as a pap for Vishnu Sipivishta (the Bald); for a pap it is whenever rice-grains are thrown (into milk or sour curds).

And as to this being so, it is because that moon is no other than King Soma, the food of the gods;--he (the Sacrificer) at that time sought to secure him, and missed him: Agni, the Giver, gives that (moon) to him, and Indra, the Bestower, bestows that one upon him; Indra and Agni give that (moon, Soma) as a sacrifice to him, and that sacrifice given by Indra and Agni he offers. And as to why (he offers) to Vishnu, the Bald, it is because Vishnu is the sacrifice; and as to why to the Bald (sipivishta),--it is that his missing him whom he sought to secure is the bald part (? sipita) of the sacrifice, hence to the Bald one. And on this occasion he should give (to the priests) as much as he is able to give, for no oblation, they say, should be without a dakshinâ. And let him observe the fast just (on the day) when he (the moon) does not rise.