Little is known about the life of R. Leib, one of the earliest chassidim of the Alter Rebbe. We know that he lived in Mogilov, Ukraine, on the border with the Turkish Ottoman Empire (to differentiate it from the other Mogilov in White Russia).
When R. Mendel Horodoker and other leading chassidic figures traveled to Eretz Yisrael in 5537, the Alter Rebbe accompanied them until Mogilov. R. Leib met the Alter Rebbe at this time and became a chossid of his, traveling back to Liozna to study further with him. Many of the Alter Rebbe’s early maamorim were published based on R. Leib’s manuscripts, and he was the leader of the Chassidim in his area, who were distant from the Alter Rebbe’s chatzer.
In his youth, R. Leib didn't take notice of the advance of Chassidus as he was deeply engrossed in Torah. However, when the Alter Rebbe, then just a student of R. Mendel Horodoker, stayed in his town and paskened a complex shailah in a wondrous manner, he posed his own dilemmas to him and became his chossid. He returned with the Alter Rebbe to Liozna, becoming one of his first chassidim, and he spent three years there.
When asked what he learned in that time, he said, "For forty years, I studied Torah lishma, and I thought only about Hashem and the Torah, but I never considered where I stand. In Liozna, I was shown how a path to think about one's own spiritual state. And for three years, I worked on myself."
(ספר השיחות תרצ"ט ע' 336)
As a result of the R. Leib's teaching of Chassidus, one talented yungerman began to dedicate himself to the study of Chassidus and davening at length in the style of Chabad. His friends, who were chassidim of other Rebbes, taunted this yungerman and said that while his new Rebbe is surely great, miracles are only found by their Rebbe. The yungerman was pained by their words and he deliberated whether to tell R. Leib about it.
Several weeks later, a shliach from the Alter Rebbe delivering money to Eretz Yisroel visited their city, and he brought with him a letter for R. Leib about how to guide each of the Chabad yungeleit. Regarding this particular yungerman the Alter Rebbe wrote, "It is fit to draw him close, and is necessary to relieve his pain. This will be a sign for him and a miracle for others."
When the yungerman heard what the Alter Rebbe had written about him, he began to cry. When questioned, he related the conversation he had with his friends.
"Now I understand the Rebbe's words," said R. Leib, "Is there a greater miracle then to take a 'block of wood' and convert it into a mentch..."
(אגרות קודש ריי"צ ח"ב ע' 441)
