Yoga Sutras of Patanjali · 2.46
स्थिरसुखमासनम् ॥४६॥
sthira-sukham āsanam
Asana is a posture that is steady and comfortable.
— Yoga Sutras of Patanjali 2.46
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).