Bhagavad Gita: Chapter 2, Verse 26

अथ चैनं नित्यजातं नित्यं वा मन्यसे मृतम् ।
तथापि त्वं महाबाहो नैनं शोचितुमर्हसि ॥ २-२६ ॥

atha cainaṁ nitya-jātaṁ nityaṁ vā manyase mṛtam
tathāpi tvaṁ mahā-bāho nainaṁ śocitum arhasi 2.26

If, however, you think that the soul will always be born and die forever, you still have no reason to lament, O mighty-armed.