Praśna Upaniṣad · 1..8

विश्वरूपं हरिणं जातवेदसं परायणं ज्योतिरेकं तपन्तम् । सहस्ररश्मिः शतधा वर्तमानः प्राणः प्रजानामुदयतेष सूर्यः ॥

viśvarūpaṃ hariṇaṃ jātavedasaṃ parāyaṇaṃ jyotirekaṃ tapantam | sahasraraśmiḥ śatadhā vartamānaḥ prāṇaḥ prajānāmudayateṣa sūryaḥ ||

Of universal forms, the golden deer, Jātavedas, the supreme refuge, the one light that warms, the one of a thousand rays, existing in a hundred forms, the Prāṇa of creatures, rises this sun.

This is the Ṛgveda verse cited (though slightly modified). It is a complex mantra describing the sun with multiple epithets:

Hariṇa — “the golden deer.” The sun is like a swift deer that crosses the sky, fast and unreachable. It also suggests beauty and grace.

Jātavedas — “the one who knows all the born.” The sun is witness to all actions, conscious of everything that happens on earth.

Parāyaṇa — “the supreme refuge.” The sun is the ultimate destination of those who follow the northern path (uttara-mārga), the path of the gods.

Sahasraraśmi — “the one of a thousand rays.” Thousand indicates infinity. Its rays touch all corners of the universe.

Prāṇaḥ prajānām — “the Prāṇa of creatures.” The sun is not just a burning mass of gas, but the source of life for all that breathes.

The yogī meditates on this inner sun, the ātma-jyoti, the light of the Self that shines in the hṛdaya (spiritual heart).