Sifrei Devarim 178/ספרי דברים קע״ח

22. “Now, if you should say in your heart: how shall we know . . .” (Dt. 18:21)?In the future, you will say:How shall we know the truth of the matter?For Jeremiah said:“Look! All the utensils of the House of HASHEMwill be deported to Babylonia!” (cf. Jer. 27:22).But Hananiah said:“Look! All the utensils of the House of HASHEMwill be returned from Babylonia!” (Jer. 27:16)—.and I don’t know whom to believe!3. The Teaching states:“When the prophet speaks . . ., and the event never transpires . . .,this is the thing that HASHEM has not spoken” (Dt. 18:22).Now, of which prophetic utterancedid the All-Present really speak?The one which [the prophet] fore-toldand it actually transpired.[But as for the prophetwhose prediction did not transpire:]“That prophet has spoken in defiance” (Dt. 18:22)—he is therefore held liable to strangulationfor intentional transgression,but he bears no liabilityfor inadvertent transgression.

3“Have no fear of him” (Dt. 18:22)—don’t hesitate to testify in courtfor the prosecution.