Quotation su Numeri 21:4

(Bamidbar 21:4): "And they journeyed from Hor Hahar by way of the Red Sea to go around the land of Edom, etc." It is known that this took place later, when "the dead of the desert" had already died out and they were close to entering Eretz Yisrael. But because of their making a detour of the land of Edom, who did not allow them to pass through their land, they thought, that G-d forbid, this might take many more years. This is what caused them to speak out and to be punished severely for it.