Bhagavad Gita Chapter 2 Verse 20
भगवद् गीता अध्याय 2 श्लोक 20

न जायते म्रियते वा कदाचि
न्नायं भूत्वा भविता वा न भूयः।
अजो नित्यः शाश्वतोऽयं पुराणो
न हन्यते हन्यमाने शरीरे।।2.20।।



हिंदी अनुवाद - स्वामी तेजोमयानंद
।।2.20।। यह आत्मा किसी काल में भी न जन्मता है और न मरता है और न यह एक बार होकर फिर अभावरूप होने वाला है। यह आत्मा अजन्मा? नित्य? शाश्वत और पुरातन है? शरीर के नाश होने पर भी इसका नाश नहीं होता।।


Kumara Vaishnava Sampradaya - Commentary
For the reasons previously described, characteristics which are  natural  to
all living entities such as birth, ageing and death do  not  pertain  to  or
have any influence on the indestructible soul as  it  has  no   modification
due to its eternal nature. The  bodily  experience  has  no  affect  on  the
eternal soul thus it is spoken of as it is not born  nor  does  it  die.  It
cannot be proven that having been before a kalpa the soul is  not  going  to
exist after a kalpa. Such births and deaths at  the  beginning  and  end  of
every kalpa are told by the Agamas in  the  Vedic  scriptures  as  replacing
each Brahma who manages and  directs  the  functioning  and  maintenance  of
creation in one singular universe in the infinite celestial  firmament.  But
this reference pertains only to the physical body and does  not  affect  the
eternal soul.

The imperishable soul  which  pervades  the  physical  body  of  all  living
entities is aja or unborn and thus it is known to be  eternal  and  constant
only changing its  external  embodied   form.  The  two  characteristics  of
eternality and constancy denote that like the material substratum  known  as
prakriti even the most subtle and infinitesimal modifications in  the  stage
preceding manifestation has no ability in any  way  to  affect  the  eternal
soul.

The word purana means ancient. Etymologically it  stems  from  purapi  navah
meaning old yet new illustrating that the eternal soul although  ancient  is
experienced with every birth as ever new. Thus it has  been  clarified  that
the physical body only perishes but never can the eternal soul perish.