Patanjali Yoga Sutra 3.40

Sanskrit Sutra

उदानजयाज्जलपङ्ककण्टकादिष्वसङ्ग उत्क्रान्तिश्च॥४०॥

Swami Vivekananda's translation

By conquering the current called Udāna the Yogi does not sink in water or in swamps, he can walk on thorns etc., and can die at will.

Chapter link: Yoga Sutra Chapter 3