Patanjali Yoga Sutra 3.39

Sanskrit Sutra

बन्धकारणशैथिल्यात् प्रचारसंवेदनाच्च चित्तस्य परशरीरावेशः॥३९॥

Swami Vivekananda's translation

When the cause of bondage of the Chitta has become loosened, the Yogi, by his knowledge of its channels of activity (the nerves), enters another’s body.

Chapter link: Yoga Sutra Chapter 3