Shatapatha Brahmana 1.8.2.5

1.8.2.5

atha sammārṣṭi | yunaktyevainametadyukto yadata ūrdhvamasaṃsthitaṃ yajñasya tadvahāditi tasmātsammārṣṭi sakṛtsakṛtsammārṣṭi tristrirvā agre devebhyaḥ sammṛjanti nettathā karavāma yathā devebhya iti tasmātsakṛtsakṛtsammārṣṭyajāmitāyai jāmi ha kuryādyattriḥ pūrvaṃ triraparaṃ tasmātsakṛtsakṛtsammārṣṭi

He (the Âgnîdhra) then sweeps (the fire) together. He thereby harnesses it: 'Thus harnessed, may it convey (to the gods) what part of the sacrifice still remains unaccomplished!' thus he thinks, and for this reason he sweeps it together. He sweeps once (with the band of the fire-wood along each of the three enclosing-sticks); for thrice each time they swept for the gods on the former occasion: 'Lest we should do it in the same way as for the gods;' thus he thinks, and accordingly he sweeps once each time in order to avoid repetition (of sacrificial performance). Repetition the would undoubtedly commit, if he were to sweep thrice the first time and thrice the second: for this reason he sweeps once (along each stick).