Esther 9:20-28 (ESV)
The Feast of Purim Inaugurated
20 And Mordecai recorded these things and sent letters to all the Jews who were in all the provinces of King Ahasuerus, both near and far, 21 obliging them to keep the fourteenth day of the month Adar and also the fifteenth day of the same, year by year, 22 as the days on which the Jews got relief from their enemies, and as the month that had been turned for them from sorrow into gladness and from mourning into a holiday; that they should make them days of feasting and gladness, days for sending gifts of food to one another and gifts to the poor.
23 So the Jews accepted what they had started to do, and what Mordecai had written to them. 24 For Haman the Agagite, the son of Hammedatha, the enemy of all the Jews, had plotted against the Jews to destroy them, and had cast Pur (that is, cast lots), to crush and to destroy them. 25 But when it came before the king, he gave orders in writing that his evil plan that he had devised against the Jews should return on his own head, and that he and his sons should be hanged on the gallows. 26 Therefore they called these days Purim, after the term Pur. Therefore, because of all that was written in this letter, and of what they had faced in this matter, and of what had happened to them, 27 the Jews firmly obligated themselves and their offspring and all who joined them, that without fail they would keep these two days according to what was written and at the time appointed every year, 28 that these days should be remembered and kept throughout every generation, in every clan, province, and city, and that these days of Purim should never fall into disuse among the Jews, nor should the commemoration of these days cease among their descendants.