The Previous Lubavitcher Rebbe wrote:
Once, Reb Pinchas was deeply engrossed in a handwritten notebook. When Reb Henoch saw his son studying the manuscript so intently, he assumed that it must be a collection of Reb Pinchas’ novel insights, and he asked to see them. He expressed satisfaction that his son was finally committing his novel insights to writing.
A few days later, Reb Henoch returned the notebook, saying that the book ought to be printed and published — though it was small in size, it was of great quality. As for what he had written in his Kuntres Acharon, the brilliance was extraordinary.
Reb Pinchas replied that he was willing to publish it, with the stipulation that the preface would not mention the author’s identity. He would also print it at his own expense. The elderly gaon Reb Henoch agreed to this. He wrote an introduction to the sefer, approving its publication, but not mentioning the author’s name, and Reb Pinchas printed it at his own expense.
The sefer immediately became well known to the public. In less than four months, the entire first edition — consisting of four thousand copies — was sold out.
When the sefer arrived in Vilna, the Gaon Rav Eliyahu heard its praises. After studying it, he too praised it, saying that the contents were arranged in logical order. He added that it would be a mitzvah if this sefer were to be found in every corner of the Jewish world. The rumor persisted that the author was one of the geonim of Shklov, who insisted on anonymity because of his great humility and saintliness. During that same year, the congregations of Vilna and Shklov contributed to the cost of two additional printings.
After more than a year passed, it became known that the author of the Hilchos Talmud Torah was none other than the Alter Rebbe himself. Thus, the sefer was held even more precious by the chassidim. Though they all possessed copies, they now reprinted it a fourth time, producing a large number of copies, which they distributed in all districts of Russia. It was also distributed in neighboring countries, in the Holy Land, and in countries between Russia and the Holy Land.