Katha Upanishad Verse 1.1.6
Nachiketas reminds his father of the transience of human life to encourage him to be truthful and fulfill his vow. He uses the analogy of grain to illustrate the cycle of birth, death, and rebirth, emphasizing that while the body is ephemeral, Truth remains constant.
Sanskrit Verse
अनुपश्य यथा पूर्वे प्रतिपश्य तथापरे ।
सस्यमिव मर्त्यः पच्यते सस्यमिवाजायते पुनः ॥ ६ ॥
Transliteration
anupaśya yathā pūrve pratipaśya tathāpare ।
sasyamiva martyaḥ pacyate sasyamivājāyate punaḥ ॥ 6 ॥
Translation
Look back to those who lived before and look to those who live now. Like grain the mortal decays and like grain again springs up (is reborn).

Muni's Play