Aitareya Upanishad 1.1.1

When this universe did not exist, then at first ‘Soul’ merely existed. There was not even a flicker. Soul viewed and reflected, perceived all in detail in the thought process as to how to create various features of creation.

आत्मा वा इदमेक एवाग्र आसीन्नान्यत्किञ्चचन । स ईक्षत लोकान्नु सृजा इति ॥ १ ॥

atma va idameka evagra asit nanyat kincana misat
sa iksata lokan nu srija iti