Eruvin 43B

ואסור לשתות יין כל ימות החול.

However, he is prohibited to drink wine on all weekdays, in case the Messiah has come and he has not yet been informed.

אי אמרת בשלמא יש תחומין ⁠— היינו דבשבתות ובימים טובים מותר. אלא אי אמרת אין תחומין, בשבתות ובימים טובים אמאי מותר?

The Talmud clarifies: Granted, if you say that the prohibition of Shabbat limits applies above 10 handbreadths, that is why on Shabbat and Festivals he is permitted to drink wine, for the Messiah will certainly not arrive from outside the Shabbat limit on those days. But if you say that the prohibition of Shabbat limits does not apply above 10 handbreadths, why is he permitted to drink wine on Shabbat and Festivals?

שאני התם, דאמר קרא: ״הנה אנכי שלח לכם את אליה הנביא וגו׳״, והא לא אתא אליהו מאתמול.

The Talmud answers: It is different there, as the verse stated: “Behold I will send you Elijah the prophet, before the coming of the great and dreadful day of YHWH; and he should turn the heart of the fathers to the children, and the heart of the children to their fathers” (Malachi 3:23–24). This verse teaches that Elijah will arrive the day before the coming of the Messiah. Since Elijah did not come the previous day, the Messiah will not come today, and therefore he may drink.

אי הכי, בחול כל יומא ויומא נמי לישתרי, דהא לא אתא אליהו מאתמול? אלא אמרינן: לבית דין הגדול אתא. הכא נמי לימא: לבית דין הגדול אתא?

The Talmud rejects this argument: If so, on weekdays, too, he should be permitted to drink wine each and every day, as Elijah did not arrive the previous day. Rather, the reason for the prohibition on weekdays must be that we say that Elijah may already have arrived at the Great Court, but it has not yet become a matter of public knowledge. Likewise, here too we should say that Elijah already arrived the previous day at the Great Court, on Friday or a Festival.