Yoga Sutras of Patanjali · 1.41

क्षीणवृत्तेरभिजातस्येव मणेर्ग्रहीतृग्रहणग्राह्येषु तत्स्थतदञ्जनता समापत्तिः ॥४१॥

kṣīṇavṛtterabhijātasyeva maṇergrahītṛgrahaṇagrāhyeṣu tatsthatadañjanatā samāpattiḥ

When the modifications have dwindled, the mind, like a clear crystal, takes the colour of whatever is placed near it — knower, knowing, or known. This is engrossment.

— Yoga Sutras of Patanjali 1.41

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).