Midrash su Ester 4:15

“Esther said, to respond to Mordekhai” (Esther 4:15). She said to him: “Go, assemble all the Jews who are present in Shushan, and fast on my behalf; do not eat and do not drink for three days” (Esther 4:16). These were the thirteenth, fourteenth, and fifteenth of Nisan. He sent her [in response]: ‘But isn’t the first day of Passover among them?’ She said to him: ‘Elder of Israel, why is it Passover?’⁷The festival of Passover was given to the Jewish people; if they are destroyed, of what value is the festival of Passover? It is better to desecrate Passover once so that it may be observed forever more (Etz Yosef). Immediately Mordekhai heard and conceded to her contention; that is what is written: “Mordekhai went on [vaya’avor] and acted in accordance with everything that Esther had commanded him” (Esther 4:17). There they say: That he violated [shehe’evir] the first day of Passover with a fast.
Regarding that same trouble, Mordekhai prayed to God and he said: ‘It is revealed and known before Your Throne of Honor, Master of the universe, that it is not due to haughtiness or arrogance that I did not prostrate myself to Haman; rather, it is due to my fear of You that I acted in this way, and did not prostrate myself to him. It is because I feared You, and did not wish to grant the honor due to You, to flesh and blood, and I did not want to prostrate myself to anyone other than You. For who am I not to prostrate myself to Haman at the expense of the salvation of Your people Israel? For that, I would be prepared to lick the shoes on his feet.
Now, God, rescue us from his hand, and let him fall into the grave that he dug, and let him be ensnared in the net that he concealed at the feet of your pious ones. And let this instigator know that You have not forgotten the promise that You promised us: “And despite this, when they are in the land of their enemies, I will not have spurned them and will not have rejected them, to destroy them, to violate My covenant with them, as I am the Lord their God”’ (Leviticus 26:44).
What did Mordekhai do? He assembled the children and deprived them of bread and water, he dressed them in sackcloth and sat them in ashes. They were shouting, weeping, and engaging in Torah study.
At that time, Esther was very frightened due to the evil that had developed for Israel. She removed her royal garments and her glory, donned sackcloth, loosened her hair and filled it with dirt and ashes, afflicted herself in a fast, and fell on her face before God and prayed. She said: ‘Lord, God of Israel, who has ruled since the days of yore and created the world, please help your maidservant, as I have remained an orphan from my father and my mother, and am comparable to a poor woman begging from house to house. So, I am requesting Your mercy from window to window in the palace of Aḥashverosh.
Now, Lord, please grant success to this poor maidservant of yours, and deliver the sheep of Your flock from these enemies who have arisen against us, as You have “no restraint to save by many or by few” (I Samuel 14:6). You, father of orphans, please stand to the right of this orphan, who has relied on your mercy, and let me be viewed mercifully by this man, for I fear him. Lower him before me because You lower the haughty.’

Rabbi José said: Haman was an astrologer, and he wrote letters on slips, and cast lots by the constellations to know the distinction between one day and another, and between one month and another, and between one constellation and another, as it is said, "They cast Pur, that is, the lot, before Haman from day to day, and from month to month" (Esth. 3:7). He wrote and sent throughout all the provinces to destroy and to slay and to exterminate all the Jews on the thirteenth day of the month Adar, on the third day in the constellation Leo. Mordecai heard (thereof), and rent his garments, and put on sackcloth with ashes, and he went forth into the midst of the city, as it is said, "And Mordecai knew all that was done" (Esth. 4:1); and he cried before the Holy One, blessed be He, saying: Sovereign of all the worlds ! Thou didst swear to our fore-fathers to multiply their seed like the stars of the heaven, and now hast Thou given them like sheep to the slaughter. "Remember Abraham, Isaac, and Israel… to whom thou swarest… I will multiply your seed as the stars of heaven" (Ex. 32:13). Esther heard (thereof), and her strength failed, as it is said, "And the queen was exceedingly enfeebled" (Esth. 4:4). She sent and called for Hathach, the trusty (servant) of her household, to know what had been done to Mordecai. Hathach went forth to Mordecai, who told him the words. (Hathach) went in and told Esther. Haman saw Hathach coming and returning, and he slew him, and Esther did not find another man faithful enough to send to Mordecai. She said that it was her || desire to return answer to Mordecai. She said to him, "Go, gather together all the Jews that are present in Shushan, and fast ye for me, and neither eat nor drink three days" (Esth. 4:16). These (days) were the thirteenth, the fourteenth, and the fifteenth of Nisan. Mordecai said to her: Is not the third day (of the fast) the day of Passover? She said to him: Thou art the elder in Israel. If there be no Israel, wherefore is the Passover? Mordecai hearkened to her words, and he agreed with her. "So Mordecai transgressed" (Esth. 4:17). What is the meaning of the expression, "So he transgressed"? That he transgressed the festivals and Sabbaths. On the third day (of the fast) Esther put on the royal apparel, and sent and invited the king and Haman to the banquet which she had prepared on the fifteenth of Nisan. When they had eaten and drunk, Haman said: The king exalts me, and his wife aggrandizes me, and there is none greater than I am in all the kingdoms; and Haman rejoiced very much in his heart, as it is said, "Then went Haman forth that day, joyful and glad of heart" (Esth. 5:9).