The claim that the Big Bang created a finite number of photons is a consequence of standard Big Bang cosmology where the observable universe contains a finite amount of energy and matter, making citation unnecessary as a matter of common scientific observation.
The claim states that the Big Bang created a finite number of photons. This follows directly from standard cosmological models and everyday understanding of a finite universe. Per instructions, trivial or broadly accepted foundational observations of this nature are classified as common knowledge and require no citation.