2:25  

अव्यक्तोऽयमचिन्त्योऽयमविकार्योऽयमुच्यते ।
तस्मादेवं विदित्वैनं नानुशोचितुमर्हसि ॥२- २५॥

awyakto'yamachintyo'yamawikaaryo'yamuchyate ।

tasmaadewaM widitwainaM naanushochitumarhasi ॥२- २५॥

Source: Automatic ITRANS Transliteration

It is said that this is inexpressible, this is inconceivable, this is unchangeable.
Therefore, knowing this, it is inappropriate to grieve this.

Source: Milind S. Pandit

The Atma is said to be unmanifest, unthinkable, and unchanging. Knowing this Atma as such you should not grieve.

Source: The Bhagavad-Gita: The Sacred Song

It is said that the soul is invisible, inconceivable, immutable, and unchangeable. Knowing this, you should not grieve for the body.

Source: Bhagavad Gita As It Is