Srimad-Bhagavatam: Canto 6 - Chapter 1 - Verse 28

Sanskrit:

सर्वे प्रयासा अभवन् विमोघा:कृता: कृता देवगणेषु दैत्यै: ।कृष्णानुकूलेषु यथा महत्सुक्षुद्रै: प्रयुक्ता ऊषती रूक्षवाच: ॥ २८ ॥

ITRANS:

sarve prayāsā abhavan vimoghāḥkṛtāḥ kṛtā deva-gaṇeṣu daityaiḥkṛṣṇānukūleṣu yathā mahatsukṣudraiḥ prayuktā ūṣatī rūkṣa-vācaḥ

Translation:

When insignificant persons use rough words to cast false, angry accusations against saintly persons, their fruitless words do not disturb the great personalities. Similarly, all the efforts of the demons against the demigods, who were favorably situated under the protection of Kṛṣṇa, were futile.

Purport:

There is a Bengali saying that if a vulture curses a cow to die, the curse will not be effective. Similarly, accusations made by demoniac persons against devotees of Kṛṣṇa cannot have any effect. The demigods are devotees of Lord Kṛṣṇa, and therefore the curses of the demons were futile.