The [Previous Lubavitcher Rebbe describes](http://www.hebrewbooks.org/pdfpager.aspx?req=15412&pgnum=195):

> 
> "'a real cheirem as prescribed by Kabbalah' requires the following: a
>  court of **seventy-two rabbis fast for forty consecutive days** (excluding
>  Shabbos and Rosh Chodesh), with six non-fast days interspersed within
>  this period. They recite **Tikkun Chatzos** and other special prayers, and
>  certain chapters of **Tehillim** each day. They regularly immerse
>  themselves in the **mikveh**, and are careful not to speak of any subject
>  that is not holy, even in Hebrew. After the Maariv prayer at the
>  conclusion of the fortieth day of the fast — while they are still fasting
>  — they spend the whole night **studying Torah**. 
> 
> 
> While it is still night,
>  about two hours before dawn, the **Holy Ark is opened**, and the chief
>  of the court reads the text of the cheirem three times. They then sound
>  the **shofar**: tekiah shevarim teruah tekiah. They remove their shoes and sit
>  upon the ground like mourners. Afterwards, they immerse
>  themselves and daven with great devotion. They daven Minchah early,
>  and only then do they eat their meal: bread dipped in salt, and water."
> 
> 
> 

When this occurs, the person's soul is, (may G-d preserve us):

> 
> **"cut off from the source of his soul as it once
>  existed on High."**
> 
> 
> 

This has been done apparently only three times in history. To Yeravam ben Nevat, Elisha ben Avuyah (or "Acher"), and [יש"ו](https://judaism.stackexchange.com/q/6326/883).

The person to whom this is done, now having been cut off from "on High", inevitably converts to another religion, (or athiesm, possibly).

---

**My questions are:**

* What's the source for this?
* Are there sifrei kabbalah that describe this?
* What about the three people to whom this was done? Are they mentioned regarding this?
* Kabbalistically, what does it mean that their soul is "cut off from the source"?