Srimad-Bhagavatam: Canto 3 - Chapter 1 - Verse 22
Sanskrit:
मनोवीर्यवरोत्सिक्तमसृण्यमकुतोभयम् ।भीता निलिल्यिरे देवास्तार्क्ष्यत्रस्ता इवाहय: ॥ २२ ॥
ITRANS:
mano-vīrya-varotsiktamasṛṇyam akuto-bhayambhītā nililyire devāstārkṣya-trastā ivāhayaḥ
Translation:
His mental and bodily strength as well as the boon conferred upon him had made him proud. He feared death at the hands of no one, and there was no checking him. The gods, therefore, were seized with fear at his very sight, and they hid themselves even as snakes hide themselves for fear of Garuḍa.
Purport:
The asuras are generally strongly built, as described here, and therefore their mental condition is very sound, and their prowess is also extraordinary. Hiraṇyākṣa and Hiraṇyakaśipu, having received the boon that they would not be killed by any other living entity within this universe, were almost immortal, and thus they were completely fearless.