Shatapatha Brahmana 8.5.1.10

8.5.1.10

atha dakṣiṇataḥ | ṣoḍaśī stoma ojo draviṇamityekādaśākṣarā vai triṣṭuptraiṣṭubhamantarikṣaṃ catasro diśa eṣa eva vajraḥ pañcadaśastasyāsāvevādityaḥ ṣoḍaśī vajrasya bhartā sa etena pañcadaśena vajreṇaitayā triṣṭubhā dakṣiṇataḥ pāpmānamapāhata tathaivaitadyajamāna etena pañcadaśena vajreṇaitayā triṣṭubhā dakṣiṇataḥ pāpmānamapahate

Then on the right (south) side, with (Vâg. S. XV, 3), 'The sixteenfold Stoma, vigour, wealth!' The Trishtubh consists of eleven syllables, and--the air being of Trishtubh nature--there are (in the air) four quarters. The thunderbolt is fifteenfold, and yonder sun is the sixteenfold wielder of that thunderbolt: with that thunderbolt, with that Trishtubh, he (Pragâpati) drove away evil in the south; and in like manner does the Sacrificer, with that thunderbolt, with that Trishtubh, now drive away evil in the south.