Megillah 5A

שמחה, אינה נוהגת אלא בזמנה.

the rejoicing that takes place on Purim is practiced only in its designated time, the 14th of Adar.

אמר רב: מגילה בזמנה ⁠— קורין אותה אפילו ביחיד, שלא בזמנה ⁠— בעשרה. רב אסי אמר: בין בזמנה בין שלא בזמנה ⁠— בעשרה. הוה עובדא, וחש ליה רב להא דרב אסי.

§ Rav said: One may read the Megilla in its proper time, i.e., on the 14th of Adar, even privately. However, when it is read not at its proper time, e.g., when the villages advance their reading to the day of assembly, it must be read with a quorum of 10, because the enactment allowing the Megilla to be read before its proper time was only made for a community. Rav Asi disagreed and said: Both at its proper time and not at its proper time, the Megilla must be read with a quorum of 10. The Talmud relates that there was an incident where Rav had to read the Megilla on Purim, and he was concerned for this opinion of Rav Asi and gathered 10 men even though he was reading the Megilla in its proper time, on the 14th of Adar.

ומי אמר רב הכי? והאמר רב יהודה בריה דרב שמואל בר שילת משמיה דרב: פורים שחל להיות בשבת ⁠— ערב שבת זמנם. ערב שבת זמנם?! והא שבת זמנם הוא! אלא לאו הכי קאמר: שלא בזמנם כזמנם. מה זמנם ⁠— אפילו ביחיד, אף שלא בזמנם ⁠— אפילו ביחיד?

The Talmud asks: And did Rav actually say this, that when the Megilla is read not at its proper time, it can only be read with a quorum of 10? Didn’t Rav Yehuda, son of Rav Shmuel bar Sheilat, say in the name of Rav: If Purim occurs on Shabbat, Friday is the proper time for reading the Megilla? The Talmud expresses surprise with regard to the wording of Rav’s statement: Is Friday the proper time for reading the Megilla? Isn’t Shabbat itself its proper time? Rather, is it not true that this is what He said: i.e., that this is the way his statement should be understood: Reading the Megilla not at its proper time is like reading it at its proper time; just as at its proper time, it can be read even privately, so too, not at its proper time, it can be read even privately.