Kaṭha Upaniṣad 54

54

devair atrāpy etasmin vastuni vicikitsitaṃ kileti bhavata eva naḥ śrutam / tvaṃ ca mṛtyo yady asmān na sujñeyam ātmatattvam āttha kathayasi / ataḥ paṇḍitair apy avadanīyatvād vaktā cāsya dharmasya tvādṛk tvattulyo 'nyaḥ paṇḍitaś ca na labhyo 'nviṣyamāṇo 'py ayaṃ tu varo niḥśreyasaprāptihetuḥ / ato nānyo varas tulyaḥ sadṛśo 'sty etasya kaścid apy, anityaphalatvād anyasya sarvasyaivety abhiprāyaḥ ///1,1.22 //

Shankara’s Commentary:
Com.—Thus addressed, Nachiketas said, ‘I have heard from yourself that even the gods had doubt on this point and you say, Oh Death, that the true nature of the atman is not easy to know. As this cannot be known even by the learned, another, learned like you 2 to explain this, cannot be found, though sought.’ This boon also is a means to the attainment of emancipation and there is no other boon which can at all weigh with this. The meaning is that other boons bear only transitory fruits.