Midrash for Bava Metzia 55:17
במקדש ראשון דנפישי ישראל טובא דכתיב בהו (מלכים א ד, כ) יהודה וישראל רבים כחול אשר על הים לרוב בעינן כולי האי במקדש שני דלא נפישי ישראל טובא דכתיב בהו (עזרא ב, סד) כל הקהל כאחד ארבע רבוא אלפים שלש מאות וששים לא בעינן כולי האי
<b><i>MISHNAH</i></b>. NOW, UNTIL WHEN IS HE [THE FINDER] OBLIGED TO PROCLAIM IT? UNTIL HIS NEIGHBOURS MAY KNOW THEREOF: THIS IS R. MEIR'S VIEW. R. JUDAH MAINTAINED: [UNTIL] THREE FESTIVALS [HAVE PASSED], AND AN ADDITIONAL SEVEN DAYS AFTER THE LAST FESTIVAL, GIVING THREE DAYS FOR GOING HOME, THREE DAYS FOR RETURNING, AND ONE DAY FOR ANNOUNCING.<span class="x" onmousemove="('comment',' The three Festivals referred to are Passover, Weeks, and Tabernacles, when Jerusalem was visited by all Israel. This was the practice whilst the Temple stood and some time after; but v. Gemara on this. ');"><sup>15</sup></span>