Katha Upanishad - Verse 2.1.3
Text: येन रूपं रसं गन्धं शब्दान्स्पर्शाँश्च मैथुनान् । एतेनैव विजानाति किमत्र परिशिष्यते । एतद्वैतत् ॥ ३ ॥ yena rūpaṃ rasaṃ gandhaṃ śabdānsparśām̐śca maithunān | etenaiva vijānāti kimatra pariśiṣyate | etadvaitat || 3 || 3. By which alone, one knows form, taste, smell, sounds, touch and the pleasures of the sexes; what remains here unknown to that. This verily is that. Shankara’s Commentary: How is that to be known, other than the knowledge of which Brahmins do not crave anything....