Bhagavad Gita · 2.25

अव्यक्तोऽयमचिन्त्योऽयमविकार्योऽयमुच्यते।तस्मादेवं विदित्वैनं नानुशोचितुमर्हसि॥

avyakto 'yam achintyo 'yam avikāryo 'yam uchyate tasmād evaṁ viditvainaṁ nānuśhochitum arhasi

The soul is said to be invisible, inconceivable, and unchangeable. Knowing this, you should not grieve for the body.

— Bhagavad Gita 2.25

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