CHĀNDOGYA UPANISHAD · 3.17.7

आदित् प्रत्नस्य रेतसः ।
उद् वयं तमसस्परि ।
ज्योतिः पश्यन्त उत्तरम् ।
स्वः पश्यन्त उत्तरम् ।
देवं देवत्रा सूर्यम् अगन्म ज्योतिर् उत्तमम् इति ज्योतिर् उत्तमम् इति ॥

ādit pratnasya retasaḥ ।
ud vayaṃ tamasaspari ।
jyotiḥ paśyanta uttaram ।
svaḥ paśyanta uttaram ।
devaṃ devatrā sūryam aganma jyotir uttamam iti jyotir uttamam iti ॥

'Then they see (within themselves) the ever-present light of the old seed (of the world, the Sat), the highest, which is lighted in the brilliant (Brahman).' Rig-veda I, 50, 10:-- 'Perceiving above the darkness (of ignorance) the higher light (in the sun), as the higher light within the heart, the bright source (of light and life) among the gods, we have reached the highest light, yea, the highest light.'

F. Max Müller · The Upanishads, Sacred Books of the East 1 (1879)