In Temple times, the shofer was blown on shabbos, but only within the vicinity of the Temple itself. Following the destruction, and the exile of the Sages to Yavneh, some thought the practice of blowing the shofar on Shabbos should be discontinued. R. Yochanan b. Zackai disagreed, and as the story is told in Tractate Rosh Hashana, he used an unorthodox ploy to win the point
On the first post-destruction Shabbos Rosh Hashana , the masses of ordinary people came to Yavneh expecting to hear the shofar. R. Yochanan b. Zackai was presiding. "Blow the shofar," he said.
"Well, hold on," replied the other Sages. "We need to talk this over and make a decision."
"The people are here and waiting," answered R. Yochanan b. Zackai "Blow now, and we'll discuss it afterwards."
The other Sages agreed and the shofar was sounded.
Afterwards, they said, "Let's discuss how this will be handled the next time Rosh Hashana and Shabbos coincide."
Replied R. Yochanan b. Zackai: "The shofar has already been sounded in Yavnah! If we discontinue the practive the people will think we made a mistake. They will come to doubt our authority. We can't change the custom now that it has been established!"
Pretty sneaky, no?
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