Elijah the prophet said to Rav Yehuda, brother of Rav Sala Ḥasida: The world will exist no fewer than eighty-five Jubilee cycles, or 4,250 years. And during the final Jubilee, the son of David will come. Rav Yehuda said to Elijah: Will the Messiah come during the beginning of the Jubilee or during its end? Elijah said to Rav Yehuda: I do not know. Rav Yehuda asked: Will this last Jubilee cycle end before the Messiah comes or will it not yet end before his coming? Elijah said to him: I do not know. Rav Ashi says: This is what Elijah said to him: Until that time do not anticipate his coming; from this point forward anticipate his coming. Elijah did not inform Rav Yehuda of the date of the coming of the Messiah.
-Sanhedrin.97b.2