Kaṭha Upaniṣad 17

17

anupaśyālocaya vibhāvayānukrameṇa yathā yena prakāreṇa vṛtāḥ pūrve 'tikrāntāḥ pitṛpitāmahādayas tava / tān dṛṣṭrvā ca teṣāṃ vṛttam āsthātum arhasi / vartamānāś cāpare sādhavo yathā vartante tāṃś ca tathā pratipaśyālocaya / na ca teṣāṃ mṛṣākaraṇaṃ vṛttaṃ vartamānaṃ vāsti / tadviparītam asatāṃ ca vṛttaṃ mṛṣākaraṇam / na ca mṛṣābhūtaṃ kṛtvā kaścid ajarāmaro bhavati / yataḥ sasyam iva martyo manuṣyaḥ pacyate jīrṇo mriyate, mṛtvā ca sasyam ivājāyata āvirbhavati punar evam anitye jīvaloke kiṃ mṛṣākaraṇena / pālayātmanaḥ satyam / preṣaya māṃ yamāyety abhiprāyaḥ ///1,1.6 //

Shankara’s Commentary:
Com.—Remember and reflect how your deceased ancestor's father, grandfather and the rest conducted themselves; seeing them, it behoves you to travel in their path; see also how others, good men, now behave. There never was or is any falsehood in them; falsifying one’s word is the manner of bad men and none who has broken his word can ever become undecaying and immortal. What is there gained by breaking one’s word, seeing that man decays and dies like corn and is again born like corn in this, transitory world of the Jivas? The meaning is ‘protect your truth and send me to Death.’