The great Upanishadic prayer is to merge into the Solar Self. The famous Isha Upanishad ends with a chant to merge in the solar Self, which also contains the oldest reference to the “Sohum” mantra.

Arising from the surrounding darkness, seeing the higher light, We have reached the Godhead, the Divine Sun, the supreme light.

Sun, O nourisher, single seer, controller, power of the Lord of creation, remove your rays and gather up your heat that I may see your most auspicious form. The Purusha (Person) that is within the Sun, He am I.