Esther 9:25-29

25 But Esther went to the king, and the king issued written orders with the result that Haman suffered the fate he had planned for the Jews - he and his sons were hanged from the gallows.
26 That is why the holidays are called Purim. Because of Mordecai's letter and because of all that had happened to them,
27 the Jews made it a rule for themselves, their descendants, and anyone who might become a Jew, that at the proper time each year these two days would be regularly observed according to Mordecai's instructions.
28 It was resolved that every Jewish family of every future generation in every province and every city should remember and observe the days of Purim for all time to come.
29 Then Queen Esther, the daughter of Abihail, along with Mordecai, also wrote a letter, putting her full authority behind the letter about Purim, which Mordecai had written earlier.
Scripture taken from the Good News Translation - Second Edition, Copyright 1992 by American Bible Society. Used by Permission.