Taanit 31A

לאיזה שירצו יעלו.

that they may ascend to wherever they wish, i.e., they may go to Jerusalem, Bethel, or Daniel

רב מתנה אמר: יום שנתנו הרוגי ביתר לקבורה. ואמר רב מתנה: אותו יום שנתנו הרוגי ביתר לקבורה, תקנו ביבנה ״הטוב והמטיב״, ״הטוב״⁠ — שלא הסריחו, ״והמטיב״⁠ — שנתנו לקבורה.

Rav Mattana said: There was an additional salvation on this day, as it was the day that the slain of Beitar were brought to burial, several years after the battle at Beitar (see Gittin 57a). And Rav Mattana said: On the same day that the slain of Beitar were brought to burial, they instituted the blessing: Who is good and does good, at Yavne. Who is good, thanking God that the corpses did not decompose while awaiting burial, and does good, thanking God that they were ultimately brought to burial.

רבה ורב יוסף דאמרי תרוייהו: יום שפסקו מלכרות עצים למערכה. דתניא, רבי אליעזר הגדול אומר: מחמשה עשר באב ואילך תשש כוחה של חמה, ולא היו כורתין עצים למערכה, לפי שאינן יבשין.

It is Rabba and Rav Yosef who both say: The 15th of Av was the day on which they stopped chopping down trees for the arrangement of wood that burned on the altar, as it is taught in a baraita that R' Eliezer the Great says: From the 15th of Av onward, the strength of the sun grows weaker, and from this date they would not cut additional wood for the arrangement, as they would not be properly dry, and they would therefore be unfit for use in the Temple.

אמר רב מנשיא: וקרו ליה יום תבר מגל. מכאן ואילך, דמוסיף ⁠— יוסיף, ודלא מוסיף ⁠— יאסף. מאי ״יאסף״? אמר רב יוסף: תקבריה אימיה.

Rav Menashya said: And they called the 15th of Av the day of the breaking of the scythe, as from this date onward no more trees were cut down, and therefore it was a celebration for the trees. The Talmud adds: From the 15th of Av onward, when the days begin to shorten, one who adds to his nightly Torah study will add years to his life, and he who does not add [mosif] will be gathered [ye’asef]. The Talmud asks: What is the meaning of the phrase: He will be gathered? Rav Yosef said: It means that his mother will bury him, as he will be gathered to his grave (see Genesis 49:33).