Albert Barnes Commentary Esther 3:13

"And letters were sent by posts into all the king`s provinces, to destroy, to slay, and to cause to perish, all Jews, both young and old, little children and women, in one day, even upon the thirteenth [day] of the twelfth month, which is the month Adar, and to take the spoil of them for a prey." — Esther 3:13 (ASV)

Currently, the Jews keep three days—the 13th, the 14th, and the 15th of Adar—as connected with “the Feast of Purim;” but they make the 13th a fast, commemorative of the fast of Esther (Esther 4:16), and keep the feast itself on the 14th and 15th of Adar.