Yoga Sutras of Patanjali · 3.35

सत्त्वपुरुषयोरत्यन्तासङ्कीर्णयोः प्रत्ययाविशेषो भोगः परार्थत्वात्स्वार्थसंयमात्पुरुषज्ञानम्॥३५॥

sattva-puruṣayoḥ atyanta-asaṅkīrṇayoḥ pratyayāviśeṣo bhogaḥ parārthatvāt svārtha-saṁyamāt puruṣa-jñānam

Experience arises from the failure to distinguish between sattva (the luminous mind) and Purusha (the Self), though they are absolutely distinct. By sanyama on what is for the sake of the Self (and not for the sake of another), knowledge of the Purusha arises.

— Yoga Sutras of Patanjali 3.35

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).