Esther 9:20

Therefore they called these days Purim after the name of Pur. Therefore, because of the words in this letter, both what they had seen in this regard and what had reached them,

the Jews established and accepted a custom for themselves and for their seed and for all those who joined themselves to them, so that celebrating these two days according to what was written down and according to their fixed time from year to year would not pass away.

Then Queen Esther, daughter of Abihail, with Mordecai the Jew, wrote with full authority to establish this second letter about Purim.

Now these are the words of the letter which Jeremiah the prophet sent from Jerusalem to the rest of the elders of the exile, the priests, the prophets, and all the people whom Nebuchadnezzar had taken away into exile from Jerusalem to Babylon.

The Feast of Purim Is Established