Kaṭha Upaniṣad 45

45

eṣa te tubhyam agnir varo he naciketaḥ, svargyaḥ svargasādhano yam agniṃ varam avṛṇīthāḥ prārthitavānasi dvitīyena vareṇa, so 'gnir varo datta ity uktopasaṃhāraḥ / kiñ caitam agniṃ tavaiva nāmnā pravakṣyanti janāso janā ity etat / eṣa varo datto mayā caturthas tuṣṭena / tṛtīyaṃ varaṃ naciketo vṛṇīṣva / tasmin hy adatta ṛṇavān evāham ity ābhiprāyaḥ ///1,1.19 //

Shankara’s Commentary:
Com.—Oh Nachiketas, this is the fire leading to heaven that you craved for, by the second boon; and the expression ‘the boon has been granted’ should be supplied by way of concluding what has been said again, people will call this fire by thy name; this is the fourth boon which I granted being delighted with thee; Oh Nachiketas, demand the third boon. The meaning is that Death considered himself a debtor if that were not granted..