Men immersing in a Mikveh daily prior to Davening Shacharis-Part 2:
C. History of the custom and its sources and reasons in the Chassidic teaching:
The directives of the Baal Shem Tov: The Baal Shem Tov stated that one is to immerse in a Mikveh as much as possible, and especially during times of need [i.e. Baal Keri; Shabbos]. The Baal Shem Tov also stated that as a result of his constant immersions he merited to reach all of his high levels and spiritual revelations. [This teaching of the Baal Shem Tov, is what can be most attributed to the evolvement of the custom to immerse daily prior to prayer. While the Baal Shem Tov did not go as far as state that one should so on a daily basis, and also made no mention that this should be done specifically prior to prayer, nonetheless, it gave the motivation for increasing the frequency of immersion to even weekdays. It is stated in the name of Rebbe Aaron of Karlin that although immersing in a mikvah is not a mitzvah, it brings a person to levels of holiness that even the greatest mitzvah cannot bring him to.]
The teachings and directives of the Alter Rebbe: The Alter Rebbe in a famous Hasidic discourse from his Sefer Likkutei Torah states that there are three things which have the power and capability of removing all [i.e. spiritual, mental, and emotional], disturbances which we commonly experience during prayer, and the first one is the immersion in the Mikveh, as a Mikveh has ability to purify. Now, although as we already stated, we rule that Tevilas Ezra for a Baal Keri is no longer a requirement even for prayer, nonetheless, the Rishonim conclude that according to all opinions the prayer is more greatly accepted above after immersion. [From here we can learn of the importance and value of the daily immersion in a mikvah prior to prayer for the sake of purifying one’s mind and elevating the quality of one’s prayer, and especially from the state of Keri.] In Beis Rebbe it states that the Alter Rebbe accustomed his Chassidim to immerse in a mikvah prior to prayer in order so the prayer be with purity. [This is seemingly the first source that we find for the widespread custom of Chassidim to immerse daily, however, from other sources to be brought to below, it is evident that the above teaching and directive of the Alter Rebbe was not understood as a requirement for a daily immersion prior to prayer and rather simply as an encouragement for occasionally immersing prior to prayer, as they were yet to be particular to do so daily. So is also evident from a letter of the Alter Rebbe in which he lists a number of actions to be done for the sake of purity and one of them is immersing in times of need for the sake of removing impurity, which refers to Tevilas Ezra. No mention is made there of a daily immersion.]
The previous Chabad custom and widespread custom in previous times: It is evident from several sources that the custom of the daily immersion prior to prayer was not widespread in previous times, including in the generations after the Baal Shem Tov. 1) In the Sefer Mishmeres Shalom [which is dedicated to analyzing and documenting the Chasidic customs from the times of the Baal Shem Tov until his time], he writes that in addition to Chassidim being very particular in Tevilas Ezra when one is in a state of Keri, the immersion in a Mikveh prior to prayer even when one is not in the state of Keri, contains great significance, and that many of the God-fearing Jews are accustomed to not have three days pass without them immersing in a Mikveh. He further writes that his father was accustomed to immerse almost daily prior to prayer. [From here it is understood that it was not yet a widespread custom even in his time, even amongst the most scrupulous Chassidim, to be particular to immerse every single day.] 2) It states in Sefer Haminhagim, based on a Sicha of the Rebbe Rayatz, that one is to immerse in a Mikveh on Yud Tes Kisleiv. From here it is understood that it was not widespread amongst Chabad Chassidim even in the times of the Rebbe Rayatz to immerse daily prior to prayer, otherwise this directive would be superfluous. 3) Indeed, Rav Shlomo Chaim Kesselman states that in the original yeshiva of Tomchei Temimim in Lubavitch, the custom amongst its students, the Temimim, was to immerse on Mondays and Thursdays and Erev Shabbos, and not every day. This was the directive of the Rebbe Rashab to the Mashpi’im of the Yeshiva.
The Rebbe’s custom: The Rebbe’s personal custom after accepting the leadership, was not to immerse in a Mikveh daily prior to prayer, and he would only immerse on rare occasions throughout the year. Despite this personal custom, the Rebbe did encourage the Chassidim to immerse prior to prayer, especially if one is a Baal Keri, but even if one is not, and explained its basis in Halacha.
The start of the widespread custom of immersing daily: Based on all the testimony received, the custom today amongst Chabad Chassidim to immerse daily prior to prayer, seemingly began becoming widespread in the mid-1900s and eventually became widespread to the point that it is followed by everyone today. However, it is evident from testimony that other Chassidic groups outside of Chabad [i.e. Chassidei Poland] were accustomed even in previous generations to immerse daily in a Mikveh prior to prayer.
The widespread custom today amongst Chassidim is to be particular to immerse daily prior to prayer. This custom is based on the encouraged practice of previous generations to increase in immersions prior to prayer, and based on the intrinsic value that it contains based on both Halacha, and Kabbalah, for purification from Keri, and Tosefes Taharah and for purposes of Teshuvah, and to prepare oneself for service of G-d similar to a Kohen, and to refine one’s heart to feel G-dliness during prayer, and to bathe the body prior to prayer out of respect of G-d.
 See Mishmeres Shalom Kudinov 2:2; Emek Yehoshua; Likkutei Maharich; Divrei Torah [Mujnktach] 3:20; Arugas Habosem O.C. 19; Piskeiy Teshuvos 4:4
 Keser Shem Tov 1 Tzavah of Besht; Likkutei Yekarim 17a; Tzivas Harivash 1:17-19
 Parshas Ki Savo p. 86
 P. 32
 Shut Admur 11
 Kudinov 2:2
 This is based on the verse in Scripture which states that the Jewish people traveled for three days and did not find water, hence emphasizing the three days without the well of Miriam [i.e. Mikveh] should not be tolerated.
 Sefer Haminhagim p. 92
 Sefer Hasichos 5702 p. 19
 Hamashpia Rav Shlomo Chaim Kesselman 1:459-460; however, see there page 9 that Rav Shlomo Chaim and his friends are ready from a young age were accustomed to immerse every day even though the general custom in Lubavitch was to only immerse three times a week
 See Maaseh Melech p. 101; Regarding before the Nesius: See Yimei Melech 1:340; 2:906
 See Toras Menachem 9 p. 169; Igros Kodesh 11:401; 9:253; 15:88; 20:93; Sefer Hamamarim 1516 p. 481 “and also one must immerse prior to the prayer”
 See Hamashpia Rav Shlomo Chaim Kesselman 1:9, 458; Ketzos Hashulchan 2 footnote 25