Skandapurana 7.16.p8

7.16.p8

vajrodyatakaro devo devānāṃ devapuṅgavaḥ .
oṅkāra iva vedānāṃ15 teṣāmāsīt purassaraḥ . .2 1 . .
vajrāstrapāvakenendro dadāha samare ripūn .
duritāni tu sarvāṇi prāyaścittānalo yathā . .22..

The god with the thunderbolt raised in his hand, the bull among the gods, / went before them, like the syllable Om before the Vedas.
With the fire of his thunderbolt weapon Indra burned the enemies in battle, / just as the fire of expiation burns all sins.