Brihadaranyaka Upanishad 2.44

यत्र त्वस्य सर्वमात्मैवाभूत्तत्केन कं पश्येत्तत्केन कं जिघ्रेत्तत्केन कं रसयेत्तत्केन कमभिवदेत्तत्केन कं शृणुयात्तत्केन कं मन्वीत तत्केन कं स्पृशेत्तत्केन कं विजानीयात् | येनेदं सर्वं विजानाति तं केन विजानीयात् | विज्ञातारमरे केन विजानीयादिति ॥

yatra tv asya sarvam atmaivabhut tat kena kam pashyet tat kena kam jighret tat kena kam rasayet tat kena kam abhivadet tat kena kam shrinuyat tat kena kam manvita tat kena kam sprishet tat kena kam vijaniyat | yenedam sarvam vijanati tam kena vijaniyat | vijnataram are kena vijaniyad iti ||

'But when everything has become the Self, then what should one see and through what? What should one smell and through what? What should one taste and through what? What should one speak and through what? What should one hear and through what? What should one think and through what? What should one touch and through what? What should one know and through what? Through what should one know that by which all this is known? Through what, O Maitreyi, should one know the Knower?'

'परन्तु जब सब कुछ स्वयं आत्मा हो जाता है — तो किसे देखे और किससे देखे? किसे सूँघे और किससे? किसका रस ले और किससे? किससे बोले? किसे सुने? किसे मनन करे? किसे जाने? इस सब को जानने वाले को किससे जाने? हे मैत्रेयी, जिससे यह सब जाना जाता है, उस आत्मा को कैसे जाना जाए?'