Fast of 17th Tammuz

17th of Tammuz falls on Shabbos:[1]

Whenever one of the four fasts fall on Shabbos, the fast takes place after Shabbos. [Thus, if the 17th of Tammuz falls on Shabbos, the fast takes place on Sunday, the 18th of Tammuz. It is permitted to have marital relations on this Shabbos of the 17th of Tammuz according to all opinions.[2]]

The 17th of Tammuz fast day summary of Halachos

• The 17th of Tammuz is a public fast day. One is required to fast on this day due to the tragedies that occurred during this time. It is also the beginning of the three-week period of mourning. This fast is mentioned explicitly in scripture [Zecharia 8] as the “Fourth fast”. The fourth fast refers to the fast of the 17th of Tammuz which is in the fourth month.
• What occurred on the 17th of Tammuz: Five tragedies occurred on the 17th of Tammuz:

1. Moshe broke the first Luchos upon descending from the mountain and seeing the golden calf.
2. The Karban Tamid sacrifice ceased to be offered onto the altar in the period of the first Temple.
3. The walls of Yerushalayim were breached during the times of the second Temple.
4. Apotomus the Rasha burned a Torah scroll.
5. Apotomus the Rasha set up an idol in the Temple

• The purpose of a fast day: The purpose of a fast day is to arouse the hearts in true repentance after contemplating the suffering we experienced due to our evil ways. Thus, each person is to do an accounting of his soul during this time.
• Avoiding anger: One must be especially careful to avoid anger on a fast day
• When does the fast begin?  The fast begins at Alos Hashachar. This is approximately two fluctuating hours prior to sunrise. Thus, even if one was awake the entire night he must stop eating and drinking two fluctuating hours before sunrise.
• One who woke up before Alos: If one slept [even on the couch] and then woke up prior to Alos, he may not eat unless he stipulated prior to going to sleep that he plans to eat after awaking before Alos. He may however have a drink, even if he did not stipulate before going to sleep, although initially it is proper to stipulate before going to sleep even if one only plans to drink and not to eat. If one did not sleep a set sleep but rather slightly dozed off, it is considered as if he has not slept and he may continue to eat until Alos.
• May one eat a lot of food prior to a fast in order so he does not feel hungry? The Poskim rule that one may not eat more than usual prior to a fast as this defeats the entire purpose of feeling oppression on that day. Nevertheless one who is weak natured and needs to eat more in order to have strength is to do so.

Those exempt from the fast:  

• Must pregnant or nursing women fast? Pregnant and nursing women are exempt from fasting. Nevertheless the custom is for even pregnant and nursing women to fast unless they are in great pain [or feel weak] in which case they are specifically not to fast. They are likewise not required to make up the fast at a later date. [Practically, the widespread custom today is for pregnant women not to fast as they are all considered weak. They are also not required to make up the fast at a later date.]
• From what stage in pregnancy is a pregnant woman exempt from fasting? A pregnant woman that is in pain is exempt from fasting starting from the 41st day of her pregnancy. If she feels weak or in great pain then she may be lenient even prior to 40 days. If she does not feel weak or any pain at all then she is required to fast if she has not yet entered her second trimester.
• Must one fast if he is sick or weak? One who is sick is exempt from fasting. One who is old or weak is not required to fast if he receives a medical order from a doctor that the fast is detrimental to his health. He is not required to make up the fast on a later date when he feels healthy.
• One who is not sick but is in pain: One who is not sick must fast even if he is experiencing a great amount of pain.
• Women after birth: According to all opinions, a woman within 30 days of giving birth does not need to fast.
• One who is traveling: If one feels healthy, he must fast even if he is traveling that day.
• Children: All children that are above the age of Bar or Bas Mitzvah are obligated to fast. All children below the age of Bar or Bas Mitzvah are not required to fast any of the four Rabbinical fasts. One is not even required to educate the child to fast for a certain amount of hours into the day. Some Poskim however rule that a child who has reached the age of understanding the mourning is only to be allowed to eat bread and water or other simple staple food. The custom however is not like this opinion. [However, they are not to be given sweets and the like although one is not required to stop them from eating it if they are in the midst of doing so.] 

The Davening:

• The Chabad custom is to recite the Selichos within Tachanun, after Shemoneh Esrei of Shacharis. It is customarily recited while standing. This especially applies for the 13 attributes and Shema Koleinu. The Chabad custom is to omit the saying of Ashamnu within Selichos when it is recited within the prayers of Shacharis. [However, it is recited as usual within Tachanun that is recited before Selichos.]
• Concentration: Selichos must be recited slowly and with concentration. It is better to recite a lesser amount of supplications, but with proper concentration, then a larger amount without concentration. Those that are accustomed to hurriedly recite the conclusion of Selichos are to nullify their custom.
• The thirteen attributes: It is forbidden to recite the thirteen attributes without proper concentration. [It is to be recited slowly and carefully. It is to be recited aloud. Some are accustomed to count the Middos with their fingers. Some are accustomed to picture each letter of each word in their mind while reciting it.] The 13 attributes may only be read together with the Minyan. The custom is to stand while reciting it. One is not to lean while reciting it unless he is old or sick.
• Shema Koleinu: The custom is to open the ark and stand for the saying of Shema Koleinu.
• Selichos without a Minyan: It is permitted to recite Selichos without a Minyan, although he must omit certain parts, as will be explained next. If one is saying Selichos without a Minyan, he is to omit the 13 attributes of mercy. [It is not our custom in such a case to recite the 13 attributes of mercy in the tune of the Torah reading-see Halacha C in Q&A!] He is likewise to omit the Aramaic parts said within Selichos. One does not omit the verse of “Uzechor Hayom Bris Shlosh Esrei” upon saying Selichos without a Minyan.
• Avinu Malkeinu: Avinu Malkeinu is recited after Selichos, prior to “Veanachnu Lo Neida”. One continues straight to Veanchnu Lo Neida after Avinu Malkeinu and omits the short Avinu Malkeinu prayer normally recited prior to Veanachnu Lo Neida.
• The Torah portion of Vayichal is read during Shacharis.             

Aneinu:

• The prayer of Aneinu is added during Mincha Shemoneh Esrei of a fast day. It is recited within the blessing of Shomeia Tefila, prior to the words “Ki Ata Shomeia”. It is not recited during the silent Shemoneh Esrei of Shacharis or Maariv. It is however recited within the Chazan’s repetition of the Shacharis and Mincha Shemoneh Esrei. The Chazan recites Aneinu as a separate blessing between the blessings of Goal Yisrael and Rifaeinu. This applies during the Chazan’s repetition of both Shacharis and Mincha Shemoneh Esrei. However during the Chazan’s silent prayer of Shemoneh Esrei of Shacharis he does not say Aneinu, while during his silent prayer of Mincha he recites Aneinu within Shomeia Tefila just like the other people praying.
• One who forgot Aneinu: If one forgot to say Aneinu in Shomeia Tefila he has nevertheless fulfilled his obligation. If he remembered prior to finishing Shemoneh Esrei he is to recite it at the end of Davening, in Elokaiy Netzor prior to the [second] Yihyu Leratzon. Even if he remembered prior to Ritzei, he is nevertheless to continue and recite it in Elokaiy Netzor. [If he only remembered after finishing Davening then it is proper to concentrate on each word of the Chazan’s repetition and thus fulfill his obligation.]
• The meaning behind Aneinu: The Kol Bo writes the prayer of Aneinu contains 63 words which correspond to the 63 letters contained within the verse “Vayira Yaakov Meod…” The Aguda writes that it corresponds to the 63 letters of the three Avos and twelve tribes. Alternatively, it corresponds to the Divine 63 letter name of Hashem [Sheim Sag], which corresponds to Bina and Gevura. We thus recite 63 words in order to sweeten the severities of Bina.

Mincha:

• Charity: Prior to Mincha one is to give Igara Ditaanisa to charity.
• Torah reading: The Torah portion of Vayichal is read during Mincha. This is followed by the reading of the Haftorah. 
• Yehalelu: After the reading of the Haftorah, Yehalelu is recited and the Torah is returned to the Aron. This is then followed by half Kaddish. [However, there were years that the Rebbe began the Kaddish immediately after the Haftorah as is normally done by Mincha of Shabbos. However, in most years the Rebbe waited for the Sefer Torah to be returned.] 
• Aneinu: During Shemoneh Esrei of Mincha Aneinu is recited, as stated in the previous Halacha.
• Nesias Kapayim: The Chazan recites Birchas Kohanim in his repetition of Shemoneh Esrei of Mincha. Those places which are not accustomed to do Birchas Kohanim recite Elokeinu during the Chazan’s repetition. [This applies even when Mincha is being davened early, by the time of Mincha Gedolah.] Those who are accustomed to perform Nesias Kapayim daily, are to do so as well by Mincha of a fast day. [However, this only applies when Mincha is being prayed close to sunset. Some rule this to be within thirty minutes before sunset. Others rule it refers to past Plag Hamincha. Others rule it refers to Mincha Ketana. However when praying Mincha prior to Plag Hamincha Nesias Kapayim is not performed. Nevertheless, one does recite Elokeinu Velokei Avoseinu, as stated above.]
• Tachanun and Avinu Malkeinu: Tachanun and Avinu Malkeinu are recited during Mincha of a fast day.

General laws applicable on fast days:

• Rinsing the mouth: On a public fast day one does not rinse his mouth in the morning. [If, however, this is causing one discomfort he may be lenient to rinse his mouth.]
• May one brush ones teeth on a fast day? If not doing so will cause one pain or discomfort it is allowed.
• May one use mouthwash if not doing so will cause pain and discomfort? Yes, it may be used in such a case.

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[1] Michaber 550:3; Rambam Taanis 5; Mishneh Megillah 5 as explained in Rashi

[2] Ashel Avraham Butchach 550; Piskeiy Teshuvos 550:9