Reference for Megillah 27:11

מיהוה טובא הוו כדתניא הרבה נביאים עמדו להם לישראל כפלים כיוצאי מצרים אלא נבואה שהוצרכה לדורות נכתבה ושלא הוצרכה לא נכתבה

There were actually very many, as it has been taught, Many prophets arose for Israel, double the number of [the Israelites] who came out of Egypt only the prophecy which contained a lesson for future generations was written down, and that which did not contain such a lesson was not written.

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