Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 33

Sanskrit:

तस्मादिन्द्रोऽबिभेच्छत्रोर्वज्र: प्रतिहतो यत: ।किमिदं दैवयोगेन भूतं लोकविमोहनम् ॥ ३३ ॥

ITRANS:

tasmād indro ’bibhec chatrorvajraḥ pratihato yataḥkim idaṁ daiva-yogenabhūtaṁ loka-vimohanam

Translation:

When Indra saw the thunderbolt return from the enemy, he was very much afraid. He began to wonder whether this had happened because of some miraculous superior power.

Purport:

Indra’s thunderbolt is invincible, and therefore when Indra saw that it had returned without doing any injury to Namuci, he was certainly very much afraid.