Esther 9:17-19

17They fought on the thirteenth day of the month of Adar and rested on the fourteenth, and it became a day of feasting and rejoicing.

18But the Jews in Susa had assembled on the thirteenth and the fourteenth days of the month. They rested on the fifteenth day of the month, and it became a day of feasting and rejoicing.

19This explains why the rural Jews who live in villages observe the fourteenth day of the month of Adar as a time of rejoicing and feasting. It is a holiday when they send gifts to one another.