Isa Upanishad*, dating from about 200 BC , identifies Brahman with the spirit of the Sun:
‘The face of truth remains hidden behind a circle of gold.
Unveil it, O God of light, that I who love the truth may see !
O life-giving Sun, offspring of the Lord of Creation, solitary seer of heaven !
Spread thy light and withdraw thy blinding splendour that I may behold thy radiant form :
That spirit far away within thee is my own inmost Spirit.
May life go to immortal life, may the body go to ashes,
OM
O my Soul, remember past strivings, remember !
O my Soul, remember past strivings, remember !
By the path of good lead us to final bliss,
O fire divine, thou God who knowest all ways.
Deliver us from wandering evil.
Prayers and adoration we offer unto thee.”