Midrash su Numeri 36:8

3) (Vayikra 22:2) ("Say to them: Throughout your generations, every man who will draw near, or all your seed, to the holy things that the children of Israel make holy to the L–rd, and his uncleanliness be upon him, then that soul will be cut off from before Me; I am the L–rd.") "Say to them": to those standing at Mount Sinai. "throughout your generations": that it be binding for all generations. If this was stated for the fathers, why was it stated for the sons, and if it was stated for the sons, why was it stated for the fathers? For there are (mitzvoth) which obtain with the fathers, but not with the sons; and with the sons, which do not obtain with the fathers. (For example:) What is stated for the fathers, (who did not enter Eretz Yisrael, (but not for the sons)? (Bamidbar 36:8) "And every daughter who received an inheritance from the tribes of the children of Israel" (her father having had no son) "to one of the family of the tribe of her father shall she be as a wife, so that the children of Israel will inherit, each, the inheritance of his fathers" in the midst of the children of Israel). (So that the mitzvah of tribal intermarriage applied only to those who left Egypt, but not to their children after them). And there are many mitzvoth that apply to the sons, (who entered Eretz Yisrael, i.e., those mitzvoth contingent upon the land of Eretz Yisrael), which did not apply to the fathers, (who did not enter). So that because there are (mitzvoth obtaining) with the fathers, which do not obtain with the sons, and (mitzvoth obtaining) with the sons, which do not obtain with the fathers, it must be written in respect to the fathers (i.e., "Say to them"), and it must be written in respect to the sons ("throughout your generations").

Rabbi Ze’eira began: “My lyre is for mourning, and my flute is for the voice of weepers” (Job 30:31). There it is taught: Rabban Shimon ben Gamliel said: There were no days as joyous for Israel as the fifteenth of Av and as Yom Kippur, on which the daughters of Jerusalem would go out in white borrowed garments so as not to embarrass one who did not have one. All the garments require immersion. The daughters of Israel would go out in them and dance in the vineyards.¹²⁷Mishna Taanit 4:8. It is taught: One who did not have a wife would turn to there. What would they say? ‘Young man, lift your eyes and see what you are choosing for yourself. Do not look at beauty, look at lineage.’ Likewise it says: “Emerge, daughters of Zion, and gaze at King Solomon, at the crown with which his mother crowned him on the day of his wedding, and on the day of the rejoicing of his heart” (Song of Songs 3:11). “The day of his wedding” – this is the giving of the Torah. “The day of the rejoicing of his heart” – this is the building of the Temple, may it be built speedily in our days.
Granted Yom Kippur, as it is a day of pardon and forgiveness for Israel, the day on which the last tablets were given. However, what is the fifteenth of Av? Rabbi Yaakov bar Aḥa said in the name of Rabbi Asi: It is the ideal time for chopping trees, as all the trees chopped on it do not produce a worm, and it is taught: Any wood in which a worm is found is disqualified from being atop the altar.¹²⁸Mishna Midot 2:5. Rabbi Abba bar Kahana and Rabbi Asi said in the name of Ulla in the name of Rabbi [Yehuda HaNasi]: It was then that Hoshea ben Ela canceled the sentries that Yerovam ben Nevat had deployed on the roads.¹²⁹Yerovam, king of Israel, appointed sentries to prevent the residents of his kingdom from ascending to Jerusalem for the pilgrimage festivals. Rav Kahana asked before Rav: Is it possible that he did all this good and it is written in his regard: “Shalmaneser, king of Assyria, ascended against him, [and Hoshea became his servant]” (II Kings 17:3)? Rather, it is because he removed the collar from his neck and placed it on the neck of the masses, and he did not say: All the people should ascend and pray, but rather, anyone who wishes to ascend let him ascend.¹³⁰Hoshea was punished, and the rest of his kingdom was punished as well (see II Kings 17:6), because he did not encourage them to ascend to Jerusalem and most of the people did not actually ascend. Previously it had been the king’s fault that the people did not ascend, as they could not go because of the sentries; subsequently it was the people’s fault, and therefore the entire kingdom was punished.
Rabbi Shmuel bat Naḥmani [said], and some say it in the name of Rabbi Shmuel bar Yitzḥak: [The fifteenth of Av is] the day the tribes were permitted to enter into marriage with one another, as it is stated: “And every daughter who inherits an inheritance [from the tribes of the children of Israel shall be a wife to one of the family of the tribe of her father]” (Numbers 36:8), and it is written: “And no inheritance shall pass from tribe to another tribe…” (Numbers 36:9). Is it possible for a daughter to inherit [from] two tribes? Rather, say on this basis, her father was from one tribe and her mother from another tribe.¹³¹The verse refers to a daughter who inherits “from the tribes of the children of Israel,” implying that her parents were from different tribes. But then the verse goes on to state that a woman cannot marry a man from a different tribe. The Sages understood this to mean that it was only in the first generation when Israel entered the land that women could not marry men from other tribes. The date when it was officially determined that from then on it was permissible was the fifteenth of Av.
The Rabbis said: [It is] the day the tribe of Benjamin was permitted to enter the congregation, as it is written: “Cursed is one who gives a woman to Benjamin” (Judges 21:18). Rabbi Yoḥanan said: They read a verse and drew them near, they read a verse and distanced them. They read a verse and drew them near: “A nation and an assembly of nations shall be from you” (Genesis 35:11).¹³²When God promised this to Jacob, Benjamin had not yet been born, meaning that it was necessary to ensure that Benjamin would procreate. They read a verse and distanced them: “Ephraim and Manasseh will be like Reuben and Simeon for me” (Genesis 48:5) – as they are not considered with their brothers.¹³³The total of twelve tribes could be achieved without Benjamin, with the addition of Ephraim and Manasseh. Rav Yehuda said that Shmuel said: It was the day that the tribes were permitted [to marry each other].
Rav Matna said: It was the day that the slain of Beitar were allowed to be buried. Rabbi Eliezer the Great said: It is reasonable on the fifteenth; from that point on, the intensity of the sun wanes and they would no longer chop wood for the arrangement. Rabbi Menasya said: They called it the day of the breaking of the scythe. From that point on: One who adds, adds, and one who does not add, will be gathered.¹³⁴From this point on, the nights begin to be lengthy. Since night is a good time for Torah study, the midrash states that years of life will be added for one who adds to his hours of Torah study. One who does not will die young.
Rabbi Avin and Rabbi Yoḥanan said: It is the day that the digging for those who died in the wilderness was halted. Rabbi Levi said: Every eve of the ninth of Av, Moses would dispatch a herald to the entire camp, saying: ‘Go out and dig,’ and they would go out and dig graves and sleep in them. In the morning, he would dispatch a herald saying: ‘Rise and separate the dead from the living,’ and they would stand and take themselves out. Fifteen thousand and more were subtracted,¹³⁵Each year for a total of six hundred thousand. In the fortieth year, the last one, they did so and found themselves intact. They said: It appears that we were mistaken in our calculation, and they did the same on the tenth, the eleventh, the twelfth, the thirteenth, and the fourteenth. When the moon was full, they said: It appears that the Holy One blessed be He abrogated the decree from upon us, and they then rendered it a holiday. But due to their iniquities, mourning beset this world with the destruction of the Temple twice. That is what is written: “My lyre is for mourning, and my flute is for the voice of weepers” (Job 30:31). “The people wept that night” (Numbers 14:1) – when they were exiled, Jeremiah began lamenting over them: “How does…sit solitary?” (Lamentations 1:1).

(Bamidbar 27:8) "And to the children of Israel shall you speak, saying": This tells us only of the immediate situation (i.e., that of Tzelafchad's daughters). Whence do we derive (the same for) future generations? From "And to the children of Israel shall you speak, saying: A man, if he die, and he have no son, then you shall pass his inheritance to his daughter." Rebbi says: In all instances (of inheritance) the term "giving" is used, but in this instance "passing" is the term employed. For only a daughter can "pass" an inheritance (from one tribe to another), her son and her husband inheriting her (i.e., what she has inherited from her father, who may be of a different tribe.) Whence is it derived that the father (of the deceased) precedes his brothers (i.e., the brothers of the deceased) in the inheritance? R. Yishmael was wont to say: It is written "then you shall pass over his inheritance to his daughter." Because of a daughter you pass over an inheritance from the father, and not because of the brothers. And whence is it derived that a father inherits (his son)? It follows, a fortiori, viz.: If the father's brothers who come (to inherit) only by power of the father, inherit him, then the father (himself), whose brothers come (to inherit) only by his power, how much more so should he inherit (his son)? And whence is it derived that the son's daughter stands in place of the son? It follows a fortiori, viz.: If the daughters of Tzelafchad, who inherited only for a particular time (i.e., an exception was made in their case, for the land was apportioned only to those who had left Egypt and had died), how much more so (is this to obtain) for the succeeding generations! Whence is it derived that females stand in the place of males (in all the "inheritances" of the Torah)? It follows (inductively), viz.: Since sons inherit and the brothers of the (deceased) father inherit, then just as with sons, females are equated with males, so, with all inheritors, females are equated with males. And just as with sons, males take precedence to females, so, with all inheritors, males take precedence to females. And just as with redeemers (of land) sons are equated with their fathers, (viz. Vayikra 25:49), so, with all inheritors, sons are equated with their fathers. And whence is it derived that a daughter inherits (her mother's possessions)? It is written (Bamidbar 36:8) "And every daughter who receives an inheritance from the tribes of the children of Israel, etc." This tells me only of a daughter. Whence do I derive (the same for) a son? It follows a fortiori, viz.: If a daughter, whose power (of inheritance) is attenuated where there is a son, inherits (her mother), how much more so, a son! And whence is it derived that a man inherits his wife? From (Ibid. 27:11) "… and he shall inherit (lit.,) her." These are the words of R. Akiva. R. Yishmael says: This (derivation) is not needed. For it is already written (Ibid. 36:8) "And every daughter who receives an inheritance from the tribes of the children of Israel, etc.", and (Ibid. 7) "And an inheritance of the children of Israel shall not go around from tribe to tribe," and (Joshua 24:33) "And Elazar the son of Aaron died, and they buried him on the hill of Pinchas, his son … in the mountain of Ephraim." Now whence did Pinchas have (land) in the mountain of Ephraim? It must be that he married a woman from the children of Ephraim, who died and whom he inherited. Similarly, (I Chronicles 2:22) "And Seguv begot Yair, and he had twenty-three cities in the land of Gilad." Now whence did Yair have (land) in the land of Gilad? It must be that he married a woman from the children of Menasheh, who died and whom he inherited.