Elliot N. Dorff; Jonathan K. Crane (2016). The Oxford Handbook of Jewish Ethics and Morality. Oxford University Press. ISBN978-0190608385. "Born in Zhagory, Lithuania, in 1810, Lipkin studied as a youth with Tzvi Hirsh Braude of Salant, and under Yosef Zundel of Salant."
The first appearance of this concept is in an essay entitled "An Essay on the Topic of Reinforcing those who Learn our Holy Torah," subsequently published in a collection of essays entitled "Etz Pri" written by a student of Lipkin based on his teacher's notes. "Etz Pri - Rabbi Yisrael Salanter, Vilna 1881. First Edition". February 21, 2018. Retrieved May 20, 2019. 40 pages, cardboard binding[permanent dead link]
