Yoga Sutras of Patanjali · 1.10

अभावप्रत्ययालम्बना वृत्तिर्निद्रा ॥१०॥

abhāvapratyayālambanā vṛttirnidrā

Sleep is the modification that rests on the cognition of absence.

— Yoga Sutras of Patanjali 1.10

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).