the Jews bound themselves to establish the custom that they and their descendants and all who join them should not fail to celebrate these two days at the appointed time each and every year, according to their regulation.

Esther 8:17
In every province and every city, wherever the king's edict and decree reached, there was joy and gladness among the Jews, with feasting and celebrating. And many of the people of the land themselves became Jews, because the fear of the Jews had fallen upon them.

Esther 9:20
Mordecai recorded these events and sent letters to all the Jews in all the provinces of King Xerxes, both near and far,

Esther 9:21
to establish among them an annual celebration on the fourteenth and fifteenth days of the month of Adar

Esther 9:28
These days should be remembered and celebrated by every generation, family, province, and city, so that these days of Purim should not fail to be observed among the Jews, nor should the memory of them fade from their descendants.

The Jews ordained, and took on them, and on their seed, and on all such as joined themselves to them, so as it should not fail, that they would keep these two days according to their writing, and according to their appointed time every year;