Devimahatmya or Saptashaticandi 24.53

Devīmāhātmya or Saptaśatīcaṇḍī 24.53

tadāhaṃ bhrāmaraṃ rūpaṃ kṛtvāsaṃkhyeyaṣaṭpadam
trailokyasya hitārthāya bhaviṣyāmi mahāsuram