Full Idea
In the beginning there was Existence, One only, without a second. Some say that in the beginning there was non-existence only, and that out of that the universe was born. But how could such a thing be? How could existence be born of non-existence?
Gist of Idea
Originally there must have been just Existence, which could not come from non-existence
Source
Anon (Upan) (The Upanishads [c.950 BCE], 'Chandogya')
Book Reference
'The Upanishads', ed/tr. Prabhavananda /Manchester [Mentor 1957], p.68
A Reaction
A very rare instance of an argument in the Upanishads, arising out of a disagreement. The monotheistic religions have preferred to make God the eternal element, presumably because that raises his status, but is also explains the start as a decision.