BṚHADĀRAṆYAKA UPANISHAD · 4.3.24

यद् वै तन् न जिघ्रति जिघ्रन् वै तन् न जिघ्रति ।
न हि घ्रातुर् घ्रातेर् विपरिलोपो विद्यते ऽविनाशित्वात् ।
न तु तद् द्वितीयम् अस्ति ततो ऽन्यद् विभक्तं यज् जिघ्रेत् ॥

yad vai tan na jighrati jighran vai tan na jighrati ।
na hi ghrātur ghrāter viparilopo vidyate ’vināśitvāt ।
na tu tad dvitīyam asti tato ’nyad vibhaktaṃ yaj jighret ॥

'And when (it is said that) there (in the Sushupti) he does not smell, yet he is smelling, though he does not smell. For smelling is inseparable from the smeller, because it cannot perish. But there is then no second, nothing else different from him that he could smell.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)