Bhagavad Gita 14.9

Purity brings happiness, passion brings commotion, and ignorance, which obscures wisdom, leads to a life of failure.

सत्त्वं सुखे सञ्जयति रजः कर्मणि भारत।ज्ञानमावृत्य तु तमः प्रमादे सञ्जयत्युत॥

sattvaṃ sukhe sañjayati rajaḥ karmaṇi bhārata|jñānamāvṛtya tu tamaḥ pramāde sañjayatyuta||

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