Esther 9:18-19

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.