Halakha Ulangan 4:25: Mishneh Torah, Fasts, Abudarham, Mishneh Torah, Prayer and the Priestly Blessing & Kitzur Shulchan Arukh

All the Jewish people are accustomed nowadays to fast on the thirteenth day of Adar in remembrance of the fast observed in the days of Haman, as it is written: "Regarding their fasting and wailing" (Esther 9:31). If the thirteenth of Adar happens to coincide with the Sabbath, we observe the fast earlier, on Thursday, the eleventh. If one of the other four fast days coincides with the Sabbath, it is postponed until after the Sabbath. If it falls on Friday, it is observed on Friday. And in all of these fasts, we do not sound [trumpets] and we do not pray the neilah prayer [service]. But we do read [the section beginning with] "And Moses implored" in the Torah (Exodus 32:11) in the morning service and the afternoon service. And we eat and drink at night on all of them, except for the Ninth of Av.

And the prayer-leader goes to bring out the Torah scroll, without saying "Deity long-suffering!," and brings out the scroll and rests it on a small tower near the ark, and does not say "All sanctify" but starts with "Revealed and shown be His sovereignty" etc. And the reason for changing the location of the Torah scroll is as we said for public fast days: "And they put burnt ashes upon the ark"¹M. Taanit 2:1, as it is written "I will be with them in stress"²Psalm 91:15. And the priest, levite, and concluder recite from Parashat Vaetḥanan, Deuteronomy 4:25–40. And say the half-qaddish, and conclude with Jeremiah 8:13-9:23, And bless the concluding blessings up until "shield of David" — in the afternoon as well. And it says in Tractate Soferim that some place the case of the scroll on the ground and say "Fallen is the crown of our heads!"³ Lamentations 5:16 and recite eulogies like one whose dead are before him, and some change their place, and some descend down from their benches, and everyone wallows in ashes, and none greets another all night and all day until the people have finished their qinot.⁴Tractate Soferim 18:7

On the Ninth of Ab, the section read in the morning service is that beginning, "When thou shalt beget children" (Deuteronomy 4:25-40). The lesson from the Prophets is that beginning, "I will consume them" (Jeremiah 8:13-9:23). In the afternoon service, the sections beginning, "And Moses besought" (Exodus 32:11-14) and also (34:1-10) are read, as on the other fast-days and on those that are kept in commemoration of the calamities that befell our ancestors. These sections are read in the morning and afternoon services. The first person called up reads four verses from the section beginning, "And Moses besought." The second and third persons read from the section beginning, "Hew thee two tables of stone" till "That I am about to do with thee" (Exodus 34:1-10). On fast days appointed by the community because of existing calamities such as drought, pestilence or similar visitations, the Benedictions and Maledictions (Leviticus 26:3-46 or Deuteronomy 28:1-69) are read, so that the people, when they listen to them, may be moved to repent and their hearts be humbled.