Jeremiah 41:12
Then they took all the men, and went to fight with Ishmael the son of Nethaniah, and found him by the great waters that are in Gibeon. Then they took all the men, and went to fight with Ishmael the son of Nethaniah, and found him by the great waters that are in Gibeon.
Jeremiah 41:1-18 records the assassination of Gedaliah at Mizpah and the dispersal of the remnant of Jews left in the land by the king of Babylon, and this verse belongs to that account which explains why the Jews observed a fast in the seventh month. Gedaliah was the Jewish viceroy left by Nebuchadnezzar after the destruction of Jerusalem, and his murder is recorded in Jeremiah 41. His murder is commemorated by a fast in the seventh month, the Fast of Gedaliah on Tisri 3. It is one of four fasts commemorating events connected with the fall of Jerusalem. That fast begins at daybreak and is one of the fasts alluded to in Zechariah 8:19.