Esther 9:27-28

the Jews took it on themselves to establish the custom that they and their descendants and all who join them should without fail observe these two days every year, in the way prescribed and at the time appointed. These days should be remembered and observed in every generation by every family, and in every province and in every city. And these days of Purim should never fail to be celebrated by the Jews—nor should the memory of these days die out among their descendants.