Śatapatha Brāhmaṇa ("of a hundred paths") 7.2.2.1

7.2.2.1

atha prāyaṇīyaṃ nirvapati | tasya haviṣkṛtā vācaṃ visṛjate vācaṃ visṛjya stambayajurharati stambayajurhṛtvā pūrveṇa parigraheṇa parigṛhya likhitvāha hara tririti harati trirāgnīdhraḥ

He then prepares the Prâyanîya (opening sacrifice). With the Havishkrit of that (oblation) he releases (the Sacrificer's) speech. Having released his speech, he throws away the grass-bush (stambayagus). Having thrown away the grass-bush, and drawn the first line of enclosure, and the lines (across the mahâ-vedi), he says, 'Throw thrice!' and the Âgnîdhra throws thrice (the wooden sword).