MB6 46b: Vowing to Fast on Days One is Forbidden to Fast (570:2-3); Talmidei Chachamim and Fasting (571:1-2)
MB6 46a: Fasting in Times of Trouble (569:1-2); Chanukah or Purim Occurring in a Series of Fasts (570:1)
MB6 34a: Nacheim and Anneinu on Tisha Bav (557:1 continued); Not Eating Meat Motzei Tisha Bav (558:1)