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].
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
य एतस्मिन् महाभागाः प्रीतिं कुर्वन्ति मानवाः । नारयोऽभिभवन्त्येतान् विष्णुपक्षानिवासुराः
ya etasmin mahābhāgāḥ prītiṃ kurvanti mānavāḥ | nārayo'bhibhavantyetān viṣṇupakṣānivāsurāḥ
SB 10.8.18