Bhagavad Gita · 2.30

देही नित्यमवध्योऽयं देहे सर्वस्य भारत।तस्मात्सर्वाणि भूतानि न त्वं शोचितुमर्हसि॥

dehī nityam avadhyo 'yaṁ dehe sarvasya bhārata tasmāt sarvāṇi bhūtāni na tvaṁ śhochitum arhasi

O Bharata, the soul dwelling in the body of every being is eternal and can never be slain. Therefore, you should not grieve for any creature.

— Bhagavad Gita 2.30

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