וּבְבֹאָ֑הּ הִנֵּ֣ה בָאָ֔ה וְיָ֣דְע֔וּ כִּ֥י נָבִ֖יא הָיָ֥ה בְתוֹכָֽם׃ (ס)
when this cometh to pass—behold, it cometh—then shall they know that a prophet hath been among them.’
Rashi on Ezekiel
behold it is coming for, indeed, it is ready to come; then they will know that your words were not a jest, but that a true prophet was in their midst.