Yoga Sutras of Patanjali · 3.12

ततः पुनः शान्तोदितौ तुल्यप्रत्ययौ चित्तस्यैकाग्रतापरिणामः॥१२॥

tataḥ punaḥ śānta-uditau tulya-pratyayau cittasya ekāgratā-pariṇāmaḥ

Then again, when the rising and subsiding cognitions become equal in content, that is the transformation of one-pointedness.

— Yoga Sutras of Patanjali 3.12

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).