So Mordecai went his way
About the business he was directed to; the word used having sometimes the signification of passing over or transgressing, Jarchi interprets it of Mordecai's transgressing the command, by fasting on a festival; the letter being written on the thirteenth of Nisan, ( Esther 3:12 ) , the next day was the passover, on which he supposes the fast began; and the three days were, the fourteenth, fifteenth, and sixteenth of the month, and belonged to the feast of the passover and of unleavened bread; so the Targum:
and did according to all that Esther had commanded him;
got the Jews together, and kept a fast three days; according to the Midrash F5 they were the thirteenth, fourteenth, and fifteenth of Nisan.