Fasting for Atonement

A patron requested citations to sources in Rabbinic literature that discuss the practice of fasting in order to gain atonement for sins. Here are some sources that I found. Please, feel free to “join the conversation” by adding additional sources in the “Comments” section.
- Yerushalmi, Betsah 2:8, s.v. a[mar] R[abi] Hananyah paam ahat yatset.
- Bavli, Hagigah 22b, s.v. amru kol yamav husharu shinav mipne taaniyotav.
- Ibid., Moed Katan 25a, s.v. de-yoma had ithafikha.
- Ibid., Bava Metsia 33a, s.v. yativ Rav Hisda arbain taanita
- Shulhan Arukh, Orah Hayim, chpt.334, paragraph 26, s.v. Hagah… ve-im avar ve-hilel tsarikh le-hitanot.
- Shulhan Arukh, Yoreh De’ah, chpt.185, paragraph 4, s.v. Hagagh…ve-im pirash mimenah.
- Shulhan Arukh, Orakh Hayim, chpt.568, paragraph 4.
- Shneur Zalman, of Lyady, 1745-1813. Likute Amarim – Tanya, Igeret ha-Teshuvah, chpt.1-3.
- Vidas, Elijah ben Moses de, 16th cent. Reshit Hokhmah, shaar ha-Teshuvah.
- Ricchi, Raphael Immanuel ben Abraham Hai, 1688-1743. Mishnat Hasidim, masekhet Teshuvah.