Esther 9:21

This was done on the thirteenth day of the month Adar, and on the fourteenth day they rested and made it a day of feasting and gladness.

But the Jews who were in Susa assembled on the thirteenth and the fourteenth of the same month, and they rested on the fifteenth day and made it a day of feasting and gladness.

the Jews established and accepted a custom for themselves and for their seed and for all those who joined themselves to them, so that celebrating these two days according to what was written down and according to their fixed time from year to year would not pass away.

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