Esther 3:6-7
6 Yet having learned who Mordecai’s people were, he scorned the idea of killing only Mordecai. Instead Haman looked for a way to destroy all Mordecai’s people, the Jews, throughout the whole kingdom of Xerxes.
7 In the twelfth year of King Xerxes, in the first month, the month of Nisan, they cast the pur (that is, the lot) in the presence of Haman to select a day and month. And the lot fell on the twelfth month, the month of Adar.