sāṃkhyayoga - Verse śloka 15
śloka 15
yaṃ hi na vyathayantyete puruṣaṃ puruṣarṣabha |
samaduḥkhasukhaṃ dhīraṃ so'mṛtatvāya kalpate ||2-15||
Translation
O best of men! The steadfast person who remains equipoised in pleasure and pain, whom these cannot afflict, becomes worthy of immortality (liberation).