After the first world war, the authenticity of George Wesley Bellows's painting of the execution of the noted nurse Edith Cavell by the Germans in 1915 (an event which the artist had not personally witnessed) was questioned by the critic Joseph Pennell.
Bellows's retort? While it was true that he had not been present at the execution, "neither had da Vinci been present at the Last Supper."
Sources
R. Kenin and J. Wintle, eds., Dictionary of Biographical Quotation
