KAṬHA UPANISHAD · 1.1.29

यस्मिन्निदं विचिकित्सन्ति मृत्यो
यत्साम्पराये महति ब्रूहि नस्तत् ।
योऽयं वरो गूढमनुप्रविष्टो
नान्यं तस्मान्नचिकेता वृणीते ॥ २९॥

yasminnidaṃ vicikitsanti mṛtyo
yatsāmparāye mahati brūhi nastat ।
yo’yaṃ varo gūḍhamanupraviṣṭo
nānyaṃ tasmānnaciketā vṛṇīte ॥ 29॥

“This of which they thus debate, O Death, declare to me, even that which is in the great passage; than this boon which enters in into the secret that is hidden from us, no other chooses Nachiketas.”