Samkhya Karika 55

तत्र जरामरणकृतं दुःखं प्राप्नोति चेतनः पुरुषः ।
लिङ्गस्याविनिवृत्तेः, तस्माद् दुःखं स्वभावेन ॥ ५५ ॥

tatra jarāmaraṇakṛtaṁ duḥkhaṁ prāpnoti cetanaḥ puruṣaḥ ।
liṅgasyāvinivṛtteḥ, tasmād duḥkhaṁ svabhāvena ॥ 55 ॥

Tatra (there, in the three worlds mentioned in the previous sutra); jarā=old age; maraṇa=death; kṛtaṁ=caused by; duḥkhaṁ=suffering; prāpnoti=experiences; cetanaḥ=conscious; puruṣaḥ=Purusha; liṅgasya=of the subtle body; āvinivṛtteḥ=until deliverance (from the subtle body); tasmāt=therefore; duḥkhaṁ=suffering; svabhāvena=natural

Therein (in the three worlds), the conscious Purusha suffers pain born of old age and death until it is released from the subtle body. Thus, pain is natural in this creation.