Brachot 19 - Honor of the Sages
Rabbi Yehoshua ben Levi taught that there are twenty four cases when the court excommunicates someone for denigrating a Sage, and they are all mentioned in the Mishnah . Rabbi Elazar asked, him, "Where?" Rabbi Yehoshua answered, "Go and search." Rabbi Elazar investigated and found only three such cases. Here is one:
Akavia ben Mahalalel held that the waters to remove suspicion of unfaithfulness cannot be given to an emancipated slavewoman. They told him, "But Shemayah and Avtalyon gave such a test to a former slavewoman called Charkemit!?" He answered, "It was the like" - meaning, they, too, did not have a pure genealogy, but descended from Sennacherib. On that, they excommunicated Akavia, and after he died, they symbolically put a stone on his coffin.
Rabbi Yehudah comments, "God forbid that they excommunicated Akavia, who was the purest of Israel. Rather it was another person." What about the story above? His comment "It was the like" means that they gave her water that looked like the water of purification, but in fact it was not.
Still, he found at most three cases, and not twenty-four, as Rabbi Yehoshua taught!? - Rabbi Yehoshua made conclusions from all comparable circumstances, and held that an excommunication happened in those situations also, and Rabbi Elazar was looking only for explicit mentions of it.
Art: German Unknown Masters - Parable of the Unfaithful Servant