Esther 9:26-27

26Therefore they called these days Purim after the name of Pur. Therefore, according to all the words of this letter, and for what they had seen concerning this matter and what had happened to them,

27the Jews ordained and took upon them, and upon their seed, and upon all such as joined themselves to them, so that it should not fail, that they would observe these two days according to their writing and according to their fixed time, every year;