Shatapatha Brahmana 11.1.3

When he has performed the Full-moon sacrifice, he prepares an additional (cake) for Indra Vimridh (the repeller of scorners), and offers it in accordance with the procedure of an ishti; and when he has performed the New-moon sacrifice, he prepares an additional rice-pap for Aditi, and offers it in accordance with the procedure of an ishti.

And as to why, after performing the Full-moon sacrifice, he prepares (a cake) for Indra Vimridh, it is because Indra is the deity of the sacrifice; but the chief oblation of the Full-moon sacrifice belongs to Agni and Soma, and nothing is offered there with the formula 'To Indra (I offer) thee!' Hereby then that oblation comes to be shared by Indra, and so does the sacrifice come to be shared by Indra. And as to why (he offers) with 'To (Indra) Vimridh!' it is that by the Full-moon sacrifice he slays all scorners (mridh), all evil spirits.

And as to why, after performing the New-moon sacrifice, he prepares a pap for Aditi,--that moon doubtless is the same as King Soma, the food of the gods: when on that night he is not seen either in the east or in the west, the oblation becomes, as it were, uncertain and unfirm. Now Aditi is this earth, and she, indeed, is certain and firmly established: thereby, then, that oblation of his becomes certain and firmly established. Such, then, is the reason why he prepares additional oblations; now as to why he should not prepare them.

When, after performing the Full-moon sacrifice, he prepares an additional (cake) for Indra Vimridh, he does so in order that his sacrifice should become shared in by Indra, for every sacrifice belongs to Indra. But inasmuch as every sacrifice belongs to Indra, thereby that oblation of his, and that sacrifice, is already shared in by Indra.

And when, after performing the New-moon sacrifice, he prepares an additional pap for Aditi,--surely the New-moon sacrifice is itself an additional one; for by the Full-moon sacrifice Indra slew Vritra, and for him who had slain Vritra, the gods then prepared that additional oblation, the New-moon sacrifice: why, then, should he prepare an oblation to be added to an additional offering? Let him, therefore, not prepare the additional oblations.

When, after performing the Full-moon sacrifice, he afterwards prepares another oblation; and when, after performing the New-moon sacrifice, he afterwards prepares another oblation, he rises and defies his malicious enemy; and, indeed, unassailed and undisturbed is the prosperity of him who at full moon performs the Full-moon sacrifice, and at new moon the New-moon sacrifice.

For by performing the Full-moon sacrifice at full moon, and the New-moon sacrifice at new moon, the gods forthwith dispelled evil, and were forthwith reproduced; and, verily, he who, knowing this, performs the Full-moon sacrifice at full moon, and the New-moon sacrifice at new moon, forthwith dispels evil, and is forthwith reproduced. If he offer an additional oblation, let him give a sacrificial fee (to the priests); for no oblation, they say, should be without a dakshinâ; and for the Full and New-moon sacrifices there is that dakshinâ, to wit, the Anvâhârya (mess of rice). Thus much as to the additional oblations; now as to (the sun) rising over him.