Yoga Sutras of Patanjali · 3.31
कूर्मनाड्यां स्थैर्यम्॥३१॥
kūrma-nāḍyāṁ sthairyam
By sanyama on the tortoise channel, steadiness arises.
— Yoga Sutras of Patanjali 3.31
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).