Numbers 36:7

That the inheritance of the children of Israel may not pass about from one tribe to another: for the children of Israel shall every one keep to the inheritance of their father's tribe.

V’LO THISOV NACHALAH’ (SO SHALL NO INHERITANCE) OF THE CHILDREN OF ISRAEL MOVE FROM TRIBE TO TRIBE. Scripture was only concerned to improve the situation at that time [i.e., for the daughters of Zelophehad who had raised that problem]. For if there were [then] women in Israel [already] married to [men of] another tribe, and they [the women] inherited [a portion of the Land] at that time, or would inherit at some future time if their brothers or fathers died without sons, their inheritance would perforce move from one tribe to another [because their husbands, who were of a different tribe, or their sons, would inherit them when they died], and who can straighten out in time what they have made crooked! The Torah, furthermore, did not want to command that the sons or husbands of these women should not inherit them [if they were not of the same tribe], because it did not deem it fit to abrogate [in this case] the [regular] law of inheritance. Similarly Scripture did not concern itself with events which would occur in the future; for even if those daughters who do not possess an inheritance [before they are married] would be permitted to marry [men from] any of the tribes, yet it is possible that at some future time they might inherit some property, if [all] their brothers die in the lifetime of their father, and thus their father’s inheritance, or that of their relatives would pass on to them.
But according to the opinion of our Rabbis who interpreted: “This law — that they marry men of their father’s tribe. only applies to that particular generation,” it is possible etc. (see text) — (Kur Zahav, in the name of Aboab). that [at that time] there were no daughters who inherited a portion amongst all those who were to come into the Land [of Israel] except for the daughters of Zelophehad, and therefore [we do not find that] they [i.e., other women] asked [Moses about it as the daughters of Zelophehad did]. Scripture, then, is commanding that if anyone dies from that day onwards until the Land is divided up amongst their tribes, and his daughter inherits him, she should not marry [anyone] from another tribe, in order that when the Land is divided up, that man should not come to take himself an inheritance amongst another tribe. For the [Torah’s] concern about them [i.e., about the separate inheritance of each tribe] was greater at the time of the division of the Land [than afterwards], so that the [different] tribes should not …