Muṇḍaka Upaniṣad 2.2.6

2.2.6

kathaṃ sūryasya raśmibhiryajamānaṃ vahantītyucyate -
1.2.6
ehyehīti tamāhutayaḥ suvarcasaḥ sūryasya raśmibhiryajamānaṃ vahanti| priyāṃ vācamabhivadantyo'rcayantya eṣa vaḥ puṇyaḥ sukṛto brahmalokaḥ ||

6. Where the nerves of the body meet together as the spokes in the nave of a wheel, this Atman is within it variously horn; meditate upon “Om” as the Atman. May there be no obstacle to your going to the other side beyond darkness.

Shankara’s Commentary:
Com.—Within the heart where all nerves running through the body meet together, as the spokes in the nave of the wheel, this Atman, spoken of, dwells within, as the witness of the states of consciousness, seeing, hearing, thinking, knowing and as it were, being variously born by the modifications of the mind, such as anger, joy, etc; men in the world say ‘He has become angry, he has become “joyful”, according to the conditions of the internal sense (mind); meditate upon Atman having the syllable “Om” as your support and imagining as stated. And it has been said “the preceptor who knows must instruct the disciples.” The disciples are those who being desirous to acquire the knowledge of the Brahman, have renounced Karma and taken the road to emancipation. The preceptor gives his benediction that they may attain the Brahman without hindrance; svasti vah paraya, let Him be without hindrance to your reaching the other shore. Parastat, beyond; beyond what? Beyond the darkness of ignorance, i. e., for the realisation of the true nature of the Atman devoid of ignorance. He who should be reached after crossing the ocean of Samsara and who is the subject of the Para vidya.