Gobhilagrihyasutra 1.5

Now at the times of the new moon and of the full moon (the following ceremonies are performed).

Let him fast on that full-moon day (when the full moon rises) at the meeting (of day and night).

The following day, according to some (teachers).

And on that day on which the moon is not seen, (he should fast, considering it) as the new-moon day.

The ends of the half-months are the time for fasting, the beginnings for sacrifice.

With the sacrificial food of the new-moon sacrifice he celebrates the first half (of the month), with that of the full-moon sacrifice the second.

Full-moon is the greatest distance of sun and moon; new-moon is their nearest approach.

That day on which the moon is not seen, that he should take as the day of new-moon.

Sometimes he may also while (the moon) is (still) visible (accept it as the day of new-moon); for (already then the moon) has made its way.

The time of full-moon is reckoned in three ways: (when the full moon rises at) the meeting (of day and night), or when it rises after sunset, or when it stands high (in the sky at sunset).

Now on what day it becomes full—

The doctrine on this point has to be studied separately. One should study it, or should ascertain separately (the exact time of) the Parvan from those who know it.

Now on the day which is the fast-day, on that day, in the forenoon, having offered his morning oblation, he besmears that surface on which the fire is placed, on all sides with cow-dung.

He then gets the pieces of wood ready (which are to be put on the fire)—of Khadira or of Palâsa wood.

If Khadira or Palâsa wood cannot be obtained, it may be wood—as far as it serves the purpose—of any tree, with the exception of Vibhîdaka, Tilvaka, Bâdhaka, Nîva, Nimba, Râgavriksha, Salmali, Aralu, Dadhittha, Kovidâra, Sleshmâtaka wood.

The Barhis consists of Kusa grass cut off at the points at which the blades diverge from the main stalk.

(The blades should be) cut off near the roots at (the ceremonies directed to) the Fathers.

If that (i.e. Kusa grass) cannot be obtained, (he may take) any kind of grass, with the exception of Sûka grass, of Saccharum reed, of such grass as is apt to break, of Balbaga grass, of Mutava, of Amphidonax reed, of Suntha.

(He should get ready the following things, viz.) Âgya, rice or barley to be cooked for the sacrifice, the pot in which the oblation of cooked rice (or barley) is prepared, the pot-ladle, the Sruva, the water fetched from a hidden place—

And the other things which we shall mention in the course of (our exposition of) the ritual.

On that day he should not go away (from his house on a journey, &c.);

Even from a distant place he should return to his house.

(On that day) he may buy goods from others, but not sell (such goods).

Let him not speak much.

Let him strive to speak the truth.

In the afternoon husband and wife, after having bathed, should eat fast-day food which is pleasant to them. It should contain butter (and should be prepared) in the due way.