Quotation for Rosh Hashanah 25:12

לא סלקא דעתך דכתיב (יהושע ד, יט) והעם עלו מן הירדן בעשור לחדש ואי ס"ד דלא עייל כלל בחמשה יומי מי קא מליא

On the morrow after the Passover they ate, but not before, [which shows that] they brought the omer and only then ate. Whence then did they obtain it?"> - He [R'Kahana] replied to them: All that had not grown to a third while in the possession of the stranger [was fitting for thei use].

Tosafot on Bava Batra