KAṬHA UPANISHAD · 2.2.4

अस्य विस्रंसमानस्य शरीरस्थस्य देहिनः ।
देहाद्विमुच्यमानस्य किमत्र परिशिष्यते । एतद्वै तत् ॥ ४॥

asya visraṃsamānasya śarīrasthasya dehinaḥ ।
dehādvimucyamānasya kimatra pariśiṣyate । etadvai tat ॥ 4॥

When this encased spirit that is in the body falleth away from it, when He is freed from its casing, what is there then that remaineth? This is the thing thou seekest.