Bhagavad Gita 3.39

It is the wise man's constant enemy; it tarnishes the face of wisdom, being as insatiable as a flame of fire.

आवृतं ज्ञानमेतेन ज्ञानिनो नित्यवैरिणा।
कामरूपेण कौन्तेय दुष्पूरेणानलेन च॥

āvṛtaṃ jñānametena jñānino nityavairiṇā|
kāmarūpeṇa kaunteya duṣpūreṇānalena ca||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).