Yoga Sutra 1.31 pain is that by which living beings are struck down,

Sūtra I.31 Pain, frustration, restlessness of the body, spasmodic breathing in or out are the accompaniments of these distractions The pain is that proceeding from the self, or proceeding from living creatures, or proceeding from the gods. Pain is that by which living beings are struck down, and which they struggle to end. Frustration is the mental agitation when a desire is obstructed. Restlessness of the body is what makes it unsteady and trembling. Spasmodic breathing is inhaling the air from outside, or exhaling the abdominal air. These are the accompaniments of the distractions; they occur in one whose mind is distracted, and do not occur in one whose mind is concentrated in samādhi. Pain is that by which living beings are struck down, and to end which they struggle, they strive. It is of three kinds, the first being that proceeding from the self (ādhyātmika). What is related (adhy) …

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