Chapter 2 · The Yoga of Knowledge · Krishna said
Bhagavad Gita 2.24 — The unchanging soul
अच्छेद्योऽयमदाह्योऽयमक्लेद्योऽशोष्य एव च। नित्यः सर्वगतः स्थाणुरचलोऽयं सनातनः ॥
acchedyo'yamadāhyo'yamakledyo'śoṣya eva ca | nityaḥ sarvagataḥ sthāṇuracalo'yaṃ sanātanaḥ ||
Meaning
The soul cannot be cut, burned, wetted or dried. It is eternal, present everywhere, stable, unmoving and ever the same.