Ester 9:17-19

9:17 All of this happened on the thirteenth day of the month of Adar. They then rested on the fourteenth day and made it a day for banqueting and happiness.

The Origins of the Feast of Purim

9:18 But the Jews who were in Susa assembled on the thirteenth and fourteenth days, and rested on the fifteenth, making it a day for banqueting and happiness. 9:19 This is why the Jews who are in the rural country – those who live in rural cities – set aside the fourteenth day of the month of Adar as a holiday for happiness, banqueting, holiday, and sending gifts to one another.

Ester 9:21

9:21 to have them observe the fourteenth and the fifteenth day of the month of Adar each year