Bhagavad Gita · 8.20

परस्तस्मात्तु भावोऽन्योऽव्यक्तोऽव्यक्तात्सनातनः।यः स सर्वेषु भूतेषु नश्यत्सु न विनश्यति॥

paras tasmāt tu bhāvo 'nyo 'vyakto 'vyaktāt sanātanaḥ yaḥ sa sarveṣhu bhūteṣhu naśhyatsu na vinaśhyati

But beyond that unmanifest, there is another unmanifest existence — an eternal being that is not destroyed when all beings perish.

— Bhagavad Gita 8.20

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)