Question: When the Nazis, may their names be blotted out, stood at the gates of Eretz Yisrael, Ha-Rav Yitzchak Isaac Herzog said: there will not be a Third Destruction. What is the source for this?
Answer: Rabbi Abba said: You have no more clear sign of the end of days than that of the verse: "But you, O mountains of Israel, shall yield your produce and bear your fruit for My people Israel, for their return is near" (Yechezkel 36:8). Rashi explains: “When the Land of Israel yields its fruit bountifully, then the end of days will be near. You have no clearer sign of the end of days than that." Sanhedrin 98a. If Chazal says that there is no clearer sign, there is none! When Rabbenu Ha-Rav Tzvi Yehudah was asked what should be said to the Charedi community, which was unconvinced regarding the Redemption, he said: "We are not Karaites! We are Talmud-faithful Jews, and the Talmud itself teaches us about the revealed Final Redemption. It says that there is no more clear sign of the Final Redemption than the Land of Israel’s offering its fruit generously to the ingathering Jews!
Ha-Rav Dr. Yaakov Herzog related about his father, the Chief Rabbi of Israel, Ha-Rav Yitzchak Isaac Herzog: "…his great Emunah was that the Return to Zion in our time is the beginning of the blossoming of the Redemption of Israel. In the year 1941, when Rommel was at the gates of Eretz Yisrael, and my Father ztz"l was then visiting Washington D.C., President Roosevelt warned him not to return to Eretz Yisrael, because it was about to be conquered by the Germans. My Father responded that the prophets prophesized regarding two destructions, and not on a Third". Am Le-Badad Yishkon p. 16. Ha-Rav Herschel Schachter writes that at the time of the Israeli War of Independence. Ha-Griz Soloveitchik of Brisk wanted to leave Yerushalayim and move to Switzerland. Rav Herzog came to him and argued that he should not leave Eretz Yisrael, and that there was no need to fear the war since we have an accepted tradition that there will not be a Third Destruction. The Brisker Rav answered that he has an accepted tradition from his father that when there is shooting one flees. This seems to mean that although there is a tradition that there will not be another destruction, this principle does not apply to individuals being killed and therefore one must flee. Ikei Ha-Tzon pp. 115-116 (Rav Herzog's opinion is also brought in Kim'a Kim'a of Ha-Rav Chaim Druckman p. 144 and Ti'um Kavanot of Ha-Rav Chaim Sabato p. 98).
This principle was also cited, however, right before the Six-Day War. At that time, Ha-Rav Shlomo Goren - who then served as the Chief Rabbi of Tzahal - traveled to Australia to help raise money for the United Jewish Appeal. With the closing of the Straits of Tiran, he understood that there would be a war and hurried to return to Eretz Yisrael. The only route home was from Australia to Los Angeles, then to New York, and from there to Israel. Rav Goren spent Shabbat in Far Rockaway, New York, which is close to the airport, in order to fly out right after Shabbat. He spoke in the White Shul on Shabbat. Rav Goren's autobiography "Be-Oz Ve-Ta'atzumot" pp. 264-265. It is related elsewhere that Rav Goren said that a war with the Arabs was about to begin. The entire community started to cry and feared a second Holocaust, but Rav Goren said that there was nothing to fear since the Torah promises that there will not be a Third Destruction (Ha-Rav Chaim Jachter in the name of Ha-Rav Shaul Chill, quoted in the parashah sheet "Kol Torah" of the Torah Academy of Bergen County).