Bhagavad Gita · Chapter 13: The Field and the Knower of the Field

Bhagavad Gita 13.19

prakṛtiṃ puruṣaṃ caiva viddhyanādī ubhāvapi | vikārāṃśca guṇāṃścaiva viddhi prakṛtisaṃbhavān ||

Know that nature and spirit are both without beginning, and know that the modifications and the qualities are born of nature.

Modern context

Now the field and the knower are given their philosophical names: prakriti, nature, and purusha, spirit. Both are without beginning. Everything that changes, all the qualities and transformations, belong to nature. Spirit is the witness that does not change. Much of our suffering comes from mixing the two, taking the changes in nature for changes in what we are.