Srimad-Bhagavatam: Canto 8 - Chapter 1 - Verse 6
श्रीप्रह्लाद उवाचनेमं विरिञ्चो लभते प्रसादंन श्रीर्न शर्व: किमुतापरेऽन्ये ।यन्नोऽसुराणामसि दुर्गपालोविश्वाभिवन्द्यैरभिवन्दिताङ्घ्रि: ॥ ६ ॥
śrī-prahrāda uvācanemaṁ viriñco labhate prasādaṁna śrīr na śarvaḥ kim utāpare ’nyeyan no ’surāṇām asi durga-pāloviśvābhivandyair abhivanditāṅghriḥ
Prahlāda Mahārāja said: O Supreme Personality of Godhead, You are universally worshiped; even Lord Brahmā and Lord Śiva worship Your lotus feet. Yet although You are such a great personality, You have kindly promised to protect us, the demons. I think that such kindness has never been achieved even by Lord Brahmā, Lord Śiva or the goddess of fortune, Lakṣmī, what to speak of other demigods or common people.
The word durga-pāla is significant. The word durga means “that which does not go very easily.” Generally durga refers to a fort, which one cannot very easily enter. Another meaning of durga is “difficulty.” Because the Supreme Personality of Godhead promised to protect Bali Mahārāja and his associates from all dangers, He is addressed here as durga-pāla, the Lord who gives protection from all miserable conditions.