Bhagavad Gita 2.25

It is named the Unmanifest, the Unthinkable, and the immutable. Therefore, knowing the Spirit as such, you have no cause to grieve.

अव्यक्तोऽयमचिन्त्योऽयमविकार्योऽयमुच्यते।
तस्मादेवं विदित्वैनं नानुशोचितुमर्हसि॥

avyakto'yamacintyo'yamavikāryo'yamucyate|
tasmādevaṃ viditvainaṃ nānuśocitumarhasi||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).