The Alter Rebbe usually said two Maamorim (presumably one on each night) each year. However, there were occasions when he said three or four, and we actually have five Maamorim which were all said in the year 5564 (1804).
The Mitteler Rebbe, who was known for his lengthy and very explanatory Discourses, would often say several Maamorim even on a regular Shabbos. One Shavous he said a total of eleven Maamorim, each of them very lengthy. His uncle Reh Yehudah Leib (the Alter Rebbe’s brother, known as the Maharil) gently chided him, saying, “Nit aleh hobin dein kop!” [“Not everyone has a head like yours!”] (Beis Rebbi, Vol. 2 pp 3a.)
One year after Shacharis the Mitteler Rebbe began to say a Maamer, explaining the concepts at great length as was his custom. When he finished the Maamer, the Chassidim began to disperse but quickly relised that the Rebbe was about to begin a second Maamer. Again, the Rebbe spoke at great length and when he finished it was apparent that he was preparing himself to begin a third. Seeing this, Reb Hillel Paritcher ran to the house of the Tzemach Tzedek [who did not always attend, his father-in-law – the Mitteler Rebbe’s, Maamorim], unable to restrain himself he grabbed the Tzemach Tzedek by the beard and cried, “Mendel Mendel! Kum her on zeh vi es gist zich chassidus in gass!” [“Mendel Mendel! Come, hear and see how Chassidus is pouring out in the street!”] (Migdal Oiz, pp 187)
The Tzemach Tzedek
In the year 5607 (1847) many Chassidim came to spend Shavuos [with the Tzemach Tzedek] amongst them the most famous, Reb Hillel Paritcher and Reb Betzalel Mai’azaritz, as well as many others. After coming from the Mikveh on Eruv Shavuos, the Rebbe said a Maamer beginning “Anoichi Havyeh Eloikechoh” [“I am Heshem your G-d” the first of the Ten Commandments]. The son’s of the Rebbe spent the entire evening and night, each in his own house, reviewing the Maamer [before the guests] and before dawn Reb Bezalel repeated the entire Maamer from memory.
After Davening there was a festive meal and all the great Chassidim and Rabbonim, as well as the sons of the Rebbe, were invited… those who were not invited stood…. When all the invitees were seated the Rebbe came out of his room and sat at the table… he poured some wine into his cup, made a brocho and said L’Chaim to his sons and the other invitees, nodding his holy head to all those who stood. He began to sing and his sons – not the invitees – sang with him. It was extremely gratifying to hear their melody. Then the Rebbe rose from his chair and began to dance alone where he stood, he held a handkerchief in his hand [it was the custom of the Rabbeim to wrap their hand in a handkerchief while sayin a Maamer]. The sons of the Rebbe – but not the invitees – clapped their hands in accompaniment…
Afterwards the Tzemach Tzedek began to sing the famous nigun of the Alter Rebbe (the one of “four stanzas”) and again his sons – but not the invitees – joined him. The Rebbe cried very much and then began to say [the Maamer] Chassidus. This Maamer was an explanation of the one beginning “Anoichi Havayeh Elokechoh”, which he had said on the previous day. (As told to the Friedker Rebbe by an elderly Chossid who was present.)
The Rebbe Rashab
Reb Elyeh Simpson related that in [Yeshivas Toimchei Temimim] Lubavitch after hearing the Maamer on the eve of Shavuos, they [the bochurim in the Yeshivah] would conduct a review of the Maamer, and when day dawned they would pause to say Birchas HaShachar [the morning Brochos].
Reb Yehudah Chitrik related: In Lubavitch there was no time to be joyous all the Chassidim were very serious throughout those two days, entirely focused on reviewing the three Maamorei Chassidus that were heard from the Rebbe Rashab… Shavuos was different from all other festivals for most of the Chassidim who came for this Yom Tov were Rabbonim, Dayonim or Shochtim…
In the year 5674 (1914), Shavuos fell out on Sunday and Monday… after Minchah on Shabbos, they began to prepare to hear the Maamer from the Rebbe. They set up tables in the form of a large hollow square, which formed a barrier around the Rebbe’s seat at a table on the south side of the hall. All the Chassidim gathered around the barrier formed by the tables, just as the Jewish people gathered at the foot of Mt. Sinai, and they sang Chabad Nigunim for a long while as they awaited the arrival of the Rebbe. The Rebbe’s only son the Rebbe Rayatz also came a while before his father, and while the Rebbe said the Maamer, his son stood face to face opposite him. We saw how the Rebbe’s son cherished and carefully assimilated each syllable and each movement of the Rebbe into the essence of his soul with a sense of humble acceptance.
Between the years 5712-5730, the Rebbe would enter the Beis Hamedresh at about three o’clock am, and say a Maamer Chassidus. This was different to any other occasion, there was no talk or nigumim beforehand; the Rebbe would enter with quick steps and sit down at the head of a table on a prepared platform. After a few moments of complete and utter silence the Rebbe would begin to recite the Maamer, in the year 5725 (1965) for example he began with the words of the Medresh, “Beshoh She’olah Moshe Le’Moroim…” [“at the time when Moses went up on high… “]. When he finished he would stand, leaving quickly and without another sound. The Chassidim, young and old, would then gather to review the Maamer, which they had just heard from the Rebbe’s mouth.
בברכת קבלת התורה בשמחה ובפנמיות!