The 15th of Elul-the Founding of Tomchei Temimim:
On the fifteenth of Elul 5657 [1897; תרנ׳׳ז] the Tomchei Temimim Yeshiva was founded in Lubavitch.
Directives of the Rebbe in connection with this date:
The Shofar is blown for the first time after the Torah reading. This set of blows is referred to as Tekios Meyushav. One fulfills his Biblical obligation of hearing Shofar with hearing this set of blows. There are various subjects of laws applicable towards Shofar blowing, as elaborated on in the section entitled “Shofar”. In this Halacha only those laws and customs that relate to the blows within the prayer will be brought.
The Satan prevents the Tekios from coming out properly:
It once occurred in a community that the Baal Tokeia was unable to blow properly and the Rav of the town, Rav Mechlin, told him to turn the Shofar around and follow a certain Segula of reciting the verse of Vayehi Noam into the Shofar. After doing so the Shofar began to blow properly. The Rav responded that the Satan was standing by the entrance of the Shofar, hence preventing the sounds from being heard [and the Segula removed the Satan from the area].
The low sounds of the Rebbe’s Tekios:
A famed Chassid was once asked why the Rebbe’s Tekios on Rosh Hashanah were always so low and came out with difficulty while he heard that in Elul when the Rebbe would blow Shofar for the Rebbetzin the sounds were strong and came out with ease. The Chassid, who was a heavy set fellow, answered “If you had someone like me sitting in the hole of your Shofar wouldn’t you have difficulty blowing it?” Meaning to say that when the Shofar is being blown for the Mitzvah there are evil forces acting as an impediment to the sounds.
Making an interval prior to the Shofar blowing:
The custom amongst all Israel is to make a slight interval between the Torah reading and Shofar blowing in order to give the Baal Tokeia and congregation time to spiritually prepare themselves as explained above.
It is forbidden to eat or drink prior to Tekias Shofar and prior to hearing Kiddush. Nevertheless some Chassidic communities are accustomed to eat after Kerias Hatorah, prior to Tekias Shofar. Some are even lenient to drink at this time without hearing Kiddush. Practically this is not the Chabad custom, and we rather follow the letter of the law that prohibits eating prior to Shofar and certainly prior to Kiddush.
 Hisvadyos 1989 4/315; Hiskashrus 995
 Siddur Admur; Rambam Shofar 3/10; Maggid Mishneh ibid that so is custom in all world; Mentioned in Admur 584/9; Rama 590/9; Birkeiy Yosef 588/1; Machazik Bracha 588/1; Chaim Sheol 2 10/3 in name of Rashash; Shaareiy Teshuvah 588; Mateh Yehuda; Kisei Eliyahu 588/1; Ruach Chaim 588/1; Kaf Hachaim 588/5; M”E 585/1; See Likkutei Sichos 39 p. 43 footnote 1 that the novelty of Admur stating this in the Siddur is because he is hinting to the reason behind blowing the Shofar at this time which is to remember the sounds that were blown by Matan Torah.
The reason: In order to remember the sound of the Shofar of Matan Torah. [Likkutei Sichos ibid based on Rasag brought in Abudarham] Alternatively the reason is because based on Kabala the Tikkun of the Shofar is only to be done after Shacharis and the reading of the Torah. [Birkeiy Yosef ibid in name of Mekubalim]
Other Customs: Some have the custom to blow the Shofar before Shacharis as was the original custom [see next]. [Birkeiy Yosef 588/1; Mateh Yehuda; Kisei Eliyahu 588/1 write that this was the custom of their time although he negates the custom and says he would not hear the Shofar before Shacharis.
The original custom: The original custom was to blow the Shofar before Shacharis as Zerizin Makdimin Lemitzvos. However this was nullified due to a decree of the gentile monarchy. [Gemara R”H 32b] Hence they would blow the Shofar during Musaf as by that time the government agents were no longer there to witness. [Rashi ibid] Others however explain that the Gemara means that this change was done due to danger as the gentiles thought that we blew the Shofar as a sign of waging war. It was thus changed to be blown during Musaf as the gentiles will simply think it is part of the regular prayers and not a vouch for war. [Tosafus 32b; Levush 585; Kaf Hachaim 585/5-0]
 See the section on Shofar Chapter 3 Halacha 1C!
 M”A 585/11; Mateh Moshe 808; Mahril; Kaf Hachaim 585/48
 This story is brought in Mateh Moshe ibid [student of Marshal] in name of one of his teachers. This story occurred at prior to the 1600’s during the lifespan of the Mateh Moshe.
 Piskeiy Teshuvos 585/1; M”E 585/1; See Sdei Chemed R”H 2/31 that some make an interval prior to Kerias Hatorah; See however Otzer Minhagei Chabad p. 106 that in 770 by the Rebbe the custom was not to make any interval
 See Piskeiy Teshuvos 585/2 for a general overview of this subject
 The prohibition against eating before Shofar: See Halacha 11A for the general prohibition of eating a meal before Shofar. This especially applies in this case as since one has to make Kiddush in order to eat, and Kiddush can only be eaten in place of a meal, some Poskim rule that any amount that one will eat after Kiddush has the status of a meal which is forbidden to be eaten prior to Shofar from the letter of the law. [Beis Yitzchak 2/18; See Mahrsham 1/1 in name of Bashamayim Rosh 74]
The prohibition against eating before Kiddush once one has completed Shemoneh Esrei of Shacharis [even though one has not yet Davened Musaf]: Admur 286/4; Takanos Rav Akiva Eiger in a year of epidemic that they should make Kiddush after Tekios Meyushav; Erech Shaiy 652; Divrei Yoel 1/29; Az Nidbaru 1/10; Sdei Chemed Daled Minim 3/22; Kaf Hachaim 588/11; Mateh Efraim 588/2
 The following Poskim mention and defend this custom: Hisorerus Teshuvah 147; Olas Shmuel 82; Tzitz Eliezer 6/7; 7/32; 8/21; Az Nidbaru 1/10; See Kaf Hachaim 588/11; Mateh Efraim 588/2
 This custom is mentioned and defended in the following Poskim: Darkei Chaim Veshalom 716; Shut Hadoctor 29/98; Sefer HaChaim p. 146-147; Heishiv Moshe 19; Sdei Chemed 2/31; Beis Yisrael 2; Alef Hamagen 588/2 and Poskim mentioned there; Zichron Yehuda in name of Maharam Eish brought in Ketzie Hamateh ibid; Betzeil Hachochmah 4/147; Piskeiy Teshuvos ibid footnote 19; See Otzer Minhagei Chabad 176
The reason for this leniency: Some Poskim rule that one is never obligated in Kiddush until after Musaf [Levush; Rashal in 286] hence on R”H since the prayers end very late one can rely on their opinion in order to garner some strength. [Piskeiy Teshuvos ibid]