Beaten with his own Staff
Confuted by one's own words. An argumentam ad hominem.
“Can High Church bigotry go father than this? And how well have I since been beaten with mine own staff.” —J Wesley. (He refers to his excluding Bolzius from “the Lord's table,” because he had not been canonically baptized.)
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894