Śatapatha Brāhmaṇa ("of a hundred paths") 4.3.3.5

4.3.3.5

indro vṛtrāya vajram prajahāra | sa vṛtram pāpmānaṃ hatvā vijite 'bhaye 'nāṣṭre dakṣiṇā nināya tasmādapyetarhi yadaivaitena mādhyandinena pavamānena stuvate 'tha vijite 'bhaye 'nāṣṭre dakṣiṇā nīyante tatho evaiṣa etaiḥ pañcabhirgrahaiḥ pāpmane dviṣate bhrātṛvyāya vajram praharati sa vṛtram pāpmānaṃ hatvā vijite 'bhaye nāṣṭre dakṣiṇā nayati tasmādvā etānpañca grahāngṛhṇāti

Indra hurled the thunderbolt at Vritra; and having smitten Vritra, the wicked, and safety and peace being secured, he led forth the dakshinâs (gifts to priests). Wherefore now also, when they (the Udgâtris) chant the midday Pavamâna, and safety and peace are secured, the dakshinâs are led forth. And so, forsooth, does he now by means of those five cups of Soma hurl the thunderbolt at the wicked, hateful enemy, and having smitten Vritra, the wicked, and safety and peace being secured, he leads forth the dakshinâs. This is why he draws those five cups.