The works of Ādi Śaṅkarācārya

Muṇḍakopaniṣadbhāṣyam

Bhashya

Bhashya

अवर्णा ।स्फुलिङ्गिनी विश्वरुची च देवी लेलायमाना दहनस्य जिह्वा ।काल्याद्या विश्वरुच्यन्ता लेलायमाना अग्नेर्हविराहुतिग्रसनार्था एता किल सप्त जिह्वा ॥

In plain words

Avarṇa, Sphuliṅginī, and Viśvarucī—the flickering, luminous tongue of fire. From Kālī up to Viśvarucī, these seven constantly dancing tongues of fire are indeed designed to consume the sacred oblations.

Close to the Sanskrit

Avarṇa, Sphuliṅginī, and Viśvarucī, the shining and flickering tongue of fire. Beginning with Kālī and ending with Viśvaruci, flickering, these are indeed the seven tongues of fire intended for swallowing the oblation offerings.