Bhagavad Gita: Chapter 2/Verse 20

न जायते म्रियते वा कदाचिन्नायं भूत्वा भविता वा न भूयः ।
अजो नित्यः शाश्वतोऽयं पुराणो न हन्यते हन्यमाने शरीरे ॥२- २०॥

na jāyate mriyate vā kadācinnāyaṃ bhūtvā bhavitā vā na bhūyaḥ ।
ajo nityaḥ śāśvato'yaṃ purāṇo na hanyate hanyamāne śarīre ॥2- 20॥

This [indestructible] is not born nor does it ever die. Not having become or become, it [never ceases to be]. This primordial, everlasting, eternal, unborn is not killed when the body is being killed. 
 
Word-for-word translation

na (adverb) (indeclinable) = not

jāyate (present tense, 3rd person, singular) = it born

mriyate (present tense, 3rd person, singular) = it dies

vā (conjunction) (indeclinable) = or

kadācit (conjunction) (indeclinable) = ever

na (adverb) (indeclinable) = not

ayam (demonstrative pronoun, nominative, singular) = this

bhūtvā (gerund) (indeclinable) = having become

bhavitā (past passive participle) = become

vā (conjunction) (indeclinable) = or

na (adverb) (indeclinable) = not

bhūyas (nominative, singular) = it is [never ceases to be]

ajas (adjective) (nominative, singular) = unborn

nityas (adjective) (nominative, singular) = eternal  

śāśvatas (adjective) (nominative, singular) = everlasting

ayam (demonstrative pronoun, nominative, singular) = this

purāṇas (adjective) (nominative, singular) = primordial 

na (adverb) (indeclinable) = not

hanyate (present tense, passive, 3rd person, singular) = to be killed 

hanyamāne (passive past participle) = when being killed

śarīre (locative, singular) = when the body


Commentary

The beginning and ending parts of this verse are very clear and similar in all translations, but the middle part of this verse (bhūtvā bhavitā vā na bhūyaḥ) is very hard to unbundle. The interpretive treatment of "bhūyas" in other translations is interesting.