Esther 9:2

9:2 The Jews assembled themselves in their cities throughout all the provinces of King Ahasuerus to strike out against those who were seeking their harm. No one was able to stand before them, for dread of them fell on all the peoples.

Esther 9:27

9:27 Therefore, because of the account found in this letter and what they had faced in this regard and what had happened to them, the Jews established as binding on themselves, their descendants, and all who joined their company that they should observe these two days without fail, just as written and at the appropriate time on an annual basis.