KAṬHA UPANISHAD · 1.1.21

देवैरत्रापि विचिकित्सितं पुरा
न हि सुविज्ञेयमणुरेष धर्मः ।
अन्यं वरं नचिकेतो वृणीष्व
मा मोपरोत्सीरति मा सृजैनम् ॥ २१॥

devairatrāpi vicikitsitaṃ purā
na hi suvijñeyamaṇureṣa dharmaḥ ।
anyaṃ varaṃ naciketo vṛṇīṣva
mā moparotsīrati mā sṛjainam ॥ 21॥

“Even by the gods was this debated of old; for it is not easy of knowledge, since very subtle is the law of it. Another boon choose, O Nachiketas; importune me not, nor urge me; this, this abandon.”