Bṛhadāraṇyaka Upaniṣad ("Great Forest Teaching") 3.8.8

3.8.8

sa hovācaitadvai tadakṣaraṃ gārgi brāhmaṇā abhivadantyasthūlamanaṇvahrasvamadīrghamalohitamasnehamacchāyamatamo'vāyvanākāśamasaṅgamarasamagandhamacakṣuṣkamaśrotramavāgamano'tejaskamaprāṇamamukhamamātramanantaramabā hyaṃ na tadaśnāti kiṃcana na tadaśnāti kaścana

He said: 'O Gârgî, the Brâhmanas call this the Akshara (the imperishable). It is neither coarse nor fine, neither short nor long, neither red (like fire) nor fluid (like water); it is without shadow, without darkness, without air, without ether, without attachment, without taste, without smell, without eyes, without ears, without speech, without mind, without light (vigour), without breath, without a mouth (or door), without measure, having no within and no without, it devours nothing, and no one devours it.'