Esther 9:1, 15, 17, 19, 21

Now in the twelfth month, that is, the month of Adar, on the thirteenth day, the time came for the king’s command and his decree to be executed. On the day that the enemies of the Jews had hoped to overpower them, the opposite occurred, in that the Jews themselves overpowered those who hated them.

And the Jews who were in Shushan gathered together again on the fourteenth day of the month of Adar and killed three hundred men at Shushan; but they did not lay a hand on the plunder.

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

Therefore the Jews of the villages who dwelt in the unwalled towns celebrated the fourteenth day of the month of Adar with gladness and feasting, as a holiday, and for sending presents to one another.

to establish among them that they should celebrate yearly the fourteenth and fifteenth days of the month of Adar