If not a play then where? It has to have come from somewhere. How did people pick it up? It must be from something that was commonly read among Shakespeare studies, possible in a common review or commentary, in order to have been so heavy quoted by the Ivy League types. Robert Moses uses it in reference to Smith after his lose in the presidential election. He studied literature intensely at Yale around 1909. I am interested in getting to the exact source. Hopefully, someone can help. Thanks.
My guess is that he either quoted it somewhere outside his works or that it is a misquotation that has taken on a life of its own. It would be interesting and informative to find the source, but no one cites one. Some quotes need a famous name attached to them to give them credence. Even scholars have been duped.