Esther 9:26-27

Wherefore they called these days Purim, after the name of Pur. Therefore because of all the words of this letter, and of that which they had seen concerning this matter, and that which had come unto them, the Jews ordained, and took upon them, and upon their seed, and upon all such as joined themselves unto them, so that it should not fail, that they would keep these two days according to the writing thereof, and according to the appointed time thereof, every year