The origin of magnetic fields from moving electric charges and intrinsic spin is a fundamental definition in classical and quantum electrodynamics, making this common knowledge that requires no citation.
The claim states the foundational definition of the origin of magnetic fields in electromagnetism (Ampere's law for moving charges/currents, and quantum spin magnetic moments). This is a well-established, definitional fact taught in introductory physics textbooks, categorizing it as common knowledge under the prompt's criteria.