BṚHADĀRAṆYAKA UPANISHAD · 1.3.14

अथ चक्षुर् अत्यवहत् ।
तद् यदा मृत्युम् अत्यमुच्यत स आदित्यो ऽभवत् ।
सो ऽसाव् आदित्यः परेण मृत्युम् अतिक्रान्तस् तपति ॥

atha cakṣur atyavahat ।
tad yadā mṛtyum atyamucyata sa ādityo ’bhavat ।
so ’sāv ādityaḥ pareṇa mṛtyum atikrāntas tapati ॥

Then he carried the eye across. When the eye had become freed from death, it became Âditya (the sun). That Âditya, after having stepped beyond death, burns.

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)