Whether this fast is maintained during times of peace, and times when the Jews have their sovereignty: Rosh HaShanah 18b-19b
That people fast on the anniversary of Gedalyah's death: Nedarim 12a
Gedalyah was killed by Yishmael ben Netanyah: Rosh HaShanah 18b
The evil of Yishmael ben Netanyah's ancestors: Megillah 15a
