Esther 9:17,18

On the thirteenth day of the month Adar This is to be referred to the foregoing words, and the meaning is, the slaughter was made in the provinces on the thirteenth day of this month, when they had reason to expect they should have been destroyed themselves. On the fifteenth day of the same they rested That is, the Jews in the city of Shushan made the fifteenth day a festival, because they had liberty to avenge themselves of their enemies, not only on the thirteenth, but also on the fourteenth day, which were both days of slaughter, and therefore they rested not till the fifteenth day.