Yoga Sutras of Patanjali · 2.5

अनित्याशुचिदुःखानात्मसु नित्यशुचिसुखात्मख्यातिरविद्या ॥५॥

anityāśuci-duḥkhānātmasu nitya-śuci-sukhātma-khyātir avidyā

Ignorance is taking the impermanent for the permanent, the impure for the pure, the painful for the pleasurable, and the non-self for the Self.

— Yoga Sutras of Patanjali 2.5

Source: Sanskrit attributed to Patanjali (c. 2nd century BCE – 4th century CE). Public-domain English readings drawn from Swami Vivekananda's 'Raja Yoga' (1896) and Charles Johnston's 'The Yoga Sutras of Patanjali' (1912).