Esther 9:25-29

But when it came to the king’s attention, he commanded by letter that his wicked scheme which he had devised against the Jews was to return on his own head, and that he and his sons were to be hanged on the wooden gallows.

Therefore they called these days Purim after the name of Pur. And because of the instructions in this letter, both what they had seen in this regard and what had happened to them,

the Jews established and made a custom for themselves, their descendants, and for all those who allied themselves with them, so that they would not fail to celebrate these two days according to their regulation and according to their appointed time annually.

So these days were to be remembered and celebrated throughout every generation, every family, every province, and every city; and these days of Purim were not to be neglected by the Jews, or their memory fade from their descendants.

Then Queen Esther, daughter of Abihail, with Mordecai the Jew, wrote with full authority to confirm this second letter about Purim.