Esther 9:26-28

Therefore, because of everything written in this letter and because of all that they had been through, the Jews agreed to continue. It became a tradition for them, their children, and all future converts to remember these two days every year on the specified dates set down in the letter. These days are to be remembered and kept by every single generation, every last family, every province and city. These days of Purim must never be neglected among the Jews; the memory of them must never die out among their descendants.