(אמר) רבה בר בר חנה א"ר יוחנן יום שכלו בו מתי מדבר דאמר מר עד שלא כלו מתי מדבר לא היה דבור עם משה שנאמר (דברים ב, טז) ויהי כאשר תמו כל אנשי המלחמה למות וידבר ה' אלי אלי היה הדבור
Rabba bar bar Ḥana said that Rabbi Yoḥanan said: The fifteenth of Av was the day on which the deaths of the Jews in the wilderness ceased. The entire generation that had left Egypt had passed away, as the Master said: After the sin of the spies, on account of which the Jews of that generation were sentenced to die in the wilderness, as long as the death of the Jews in the wilderness had not ceased, God’s speech did not come to Moses, as it is stated: “And it came to pass, when all the men of war were consumed and dead from among the people, that the Lord spoke to me, saying” (Deuteronomy 2:16–17). This indicates that only then, after the last member of that generation had died, was God’s speech delivered to me, i.e., Moses, but not beforehand. When the Jews realized that the decree that God would not speak to Moses had been lifted, they established that day as a permanent day of rejoicing.
שכלו מתי מדבר - דתניא כל ארבעים שנה שהיו במדבר בכל ערב תשעה באב היה הכרוז יוצא ואומר צאו לחפור והיה כל אחד ואחד יוצא וחופר לו קבר וישן בו שמא ימות קודם שיחפור ולמחר הכרוז יוצא וקורא יבדלו חיים מן המתים וכל שהיה בו נפש חיים היה עומד ויוצא וכל שנה היו עושין כן ובשנת ארבעים שנה עשו ולמחר עמדו כולן חיים וכיון שראו כך תמהו ואמרו שמא טעינו בחשבון החדש חזרו ושכבו בקבריהן בלילות עד ליל חמשה עשר וכיון שראו שנתמלאה הלבנה בט"ו ולא מת אחד מהם ידעו שחשבון חדש מכוון וכבר מ' שנה של גזרה נשלמו קבעו אותו הדור לאותו היום יו"ט:
1 "[the day] on which the deaths ceased in the desert" - As it was taught in a braita, all 40 years that they were in the desert, every Erev Tisha B’av, the proclaimer would go out and say: let each individual go out and dig [his grave]. And every single person would go out and dig for themselves a grave, and sleep in it, in case they would die before they had dug. And the next day, the proclaimer would go out and proclaim: let the living separate themselves from the dead. And every one who had the soul of life would rise and go out [of his grave]. And every year they would do this. And in the 40th year, they did it, and the next morning everyone stood up alive. And when they saw this, they were astonished, and they said, ‘perhaps we made a mistake in calculating the month [and it is not yet Tisha B’Av].’ They returned and slept in their graves each night until the 15th, and since they saw that the moon was full on Tu [B’av] and no one had died among them, they knew that the calculation of the month was in line, and that the 40 years of the decree had been completed, they established that day as a Yom Tov.