RAV KOOK ON PARSHAT Shlach part 3/Pinchas: The Sin of Tzelofchad

"Our father died in the desert... He died because of his own sin, and he had no sons." (Num. 27:3) So begins the request of the daughters of Tzelofchad. Since there were no sons in the family, the daughters wanted to know: may we inherit his portion in the Land of Israel? Their question stumped Moses, and was referred to God Himself. The Torah doesn't tell us, but we are curious nonetheless: what was the sin for which Tzelofchad deserved to die? The text seems to imply that his transgression was an unusual one — "He died because of his own sin."