Auto da Fe
[An act of faith.] A day set apart by the Inquisition for the examination of “heretics.” Those not acquitted were burnt. The reason why inquisitors burnt their victims was, because they are forbidden to “shed blood”; an axiom of the Roman Catholic Church being, “Ecclesia non novit sanguinem ” (the church is untainted with blood).
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894