Srimad-Bhagavatam: Canto 10 - Chapter 1 - Verse 18
Sanskrit:
य एतस्मिन् महाभागा: प्रीतिं कुर्वन्ति मानवा: ।नारयोऽभिभवन्त्येतान् विष्णुपक्षानिवासुरा: ॥ १८ ॥
ITRANS:
ya etasmin mahā-bhāgāḥprītiṁ kurvanti mānavāḥnārayo ’bhibhavanty etānviṣṇu-pakṣān ivāsurāḥ
Translation:
Demons [asuras] cannot harm the demigods, who always have Lord Viṣṇu on their side. Similarly, any person or group attached to Kṛṣṇa is extremely fortunate. Because such persons are very much affectionate toward Kṛṣṇa, they cannot be defeated by demons like the associates of Kaṁsa [or by the internal enemies, the senses].