Yoga Sutras of Patanjali · 2.51

बाह्याभ्यन्तरविषयाक्षेपी चतुर्थः ॥५१॥

bāhyābhyantara-viṣayākṣepī caturthaḥ

The fourth pranayama transcends the spheres of inward and outward.

— Yoga Sutras of Patanjali 2.51

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).