Bhagavad Gita 15.16
There are two persons in the world: the perishable, which is all beings, and the unchanging imperishable.
द्वाविमौ पुरुषौ लोके क्षरश्चाक्षर एव च।
क्षरः सर्वाणि भूतानि कूटस्थोऽक्षर उच्यते॥
dvāvimau puruṣau loke kṣaraścākṣara eva ca
kṣaraḥ sarvāṇi bhūtāni kūṭastho'kṣara ucyate
Translation
There are two kinds of person in the world, the perishable and the imperishable. The perishable is all beings. The unchanging one, standing firm, is called the imperishable.
Hindi
इस लोक में दो प्रकार के पुरुष हैं, क्षर और अक्षर। सब भूत क्षर हैं, और जो कूटस्थ अपरिवर्तनशील है, वह अक्षर कहलाता है।
Commentary
The Gita now sorts reality into two. The perishable is every living being that is born and dies, while the imperishable is the unchanging witness, called kutastha, like an anvil that stays still under the hammer. Commentators differ on whether this is the soul or nature at rest, but all agree it is not the highest. 15.17 speaks of one beyond both.