Nitric acid is a strong oxidizing acid that reacts with copper to produce nitrogen oxides (such as nitrogen dioxide or nitric oxide) and copper salts rather than hydrogen gas, making this a well-established chemical fact that requires no citation.
The claim states a fundamental chemical fact about the reaction between nitric acid and copper. Because nitric acid is an oxidizing agent, the reduction of the nitrate ion is thermodynamically and kinetically favored over the reduction of protons to hydrogen gas, so H2 is not produced. As a matter of basic, everyday chemical knowledge, no specific study citation is required, and none of the retrieved papers directly test or contradict this standard textbook fact.