KAṬHA UPANISHAD · 1.1.20

येयं प्रेते विचिकित्सा मनुष्येऽस्तीत्येके नायमस्तीति चैके ।
एतद्विद्यामनुशिष्टस्त्वयाऽहं
वराणामेष वरस्तृतीयः ॥ २०॥

yeyaṃ prete vicikitsā manuṣye’stītyeke nāyamastīti caike ।
etadvidyāmanuśiṣṭastvayā’haṃ
varāṇāmeṣa varastṛtīyaḥ ॥ 20॥

“This debate that there is over the man who has passed and some say ‘This he is not’ and some that he is, that, taught by thee, I would know; this is the third boon of the boons of my choosing.”