Shana Tova. The third day of Tishrei is known as צום גדליה, the Fast of Gedalia. It is also referred to as the Fast of the Seventh Month, as Tishrei is the seventh month after Nissan.
There are opinions that the assassination of Gedalia Ben Achikam took place on Rosh Hashanah but the fast is observed on the third of Tishrei.
This incident is mentioned both in the Book of Kings as well as Chronicles, דברי הימים. Gedalia was a governor after the destruction of the First Temple, with permission from Nebuchadnezzar. Many Jews who fled, returned to the Land of Yehudah to tend their vineyards, and had a brief respite.The king of Ammon did not wish to see a revival of Jewish life. He hired a Jew, Yishmael Ben Netanya, to kill Gedalia in the town of Mitzpa.
Gedalia was warned of the plot but didn’t believe it was possible for a Jew to kill another Jew. Because this was the last hope of the rebuilding of the Temple, a fast was ordained on this date.
As always, fast days were meant for contemplation and repentance. This is most appropriate during the Ten Days of Teshuva.