Gobhilagrihyasutra 1.5.13

1.5.13

- atha yad ahar upavasatho bhavati, tad ahaḥ pūrvāhṇa eva prātarāhutiṃ hutvai 'tad agneḥ sthaṇḍilaṃ gomayena samantaṃ paryupalimpati.

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.