Adam Clarke on Esther 9:23

The Jews undertook to do as they had begun - They had already kept the fifteenth day, and some of them in the country the fourteenth also, as a day of rejoicing: Mordecai wrote to them to bind themselves and their successors, and all their proselytes, to celebrate this as an annual feast throughout all their generations; and this they undertook to do. And it has been observed among them, in all places of their dispersion, from that day to the present time, without any interruption.