Kaṭha Upaniṣad 1.14

1.14

pra te bravīmi tad u me nibodha svargyam agniṃ naciketaḥ prajānan /
anantalokāptim atho pratiṣṭhāṃ viddhi tvam etaṃ nihitaṃ guhāyām //

[Death :] 14. To thee I do declare, and do thou learn it of me— Understanding about the heavenly fire, O Naciketas ! The attainment of the infinite world, likewise too its establishment— Know thou that as set down in the secret place [of the heart].