“Mordekhai returned to the king’s gate and Haman hastened home, mourning and covering his head” (Esther 6:12). Mordekhai returned to the king’s gate; [this phrase] teaches that he returned to his sackcloth and fasting. Rabbi Ḥelbo said: Anyone who wears sackcloth and fasts does not cease to do so until his petition is fulfilled.
Mordekhai Returned to the King's Gate and Haman Hastened
Esther Rabbah 10:6