KAṬHA UPANISHAD · 1.1.19

एष तेऽग्निर्नचिकेतः स्वर्ग्यो
यमवृणीथा द्वितीयेन वरेण ।
एतमग्निं तवैव प्रवक्ष्यन्ति जनासः
तृतीयं वरं नचिकेतो वृणीष्व ॥ १९॥

eṣa te’gnirnaciketaḥ svargyo
yamavṛṇīthā dvitīyena vareṇa ।
etamagniṃ tavaiva pravakṣyanti janāsaḥ
tṛtīyaṃ varaṃ naciketo vṛṇīṣva ॥ 19॥

“This is the heavenly Flame, O Nachiketas, which thou hast chosen for the second boon; of this Flame the peoples shall speak that it is thine indeed. A third boon choose, O Nachiketas.”