Esther 9:27-28

the Jews established and imposed it upon themselves and their descendants and all who would join them, that without fail they should celebrate these two days every year, according to the written instructions and according to the prescribed time, that these days should be remembered and kept throughout every generation, every family, every province, and every city, that these days of Purim should not fail to be observed among the Jews, and that the memory of them should not perish among their descendants.