R. Mordecai Joseph Leiner of Izbica (d. 1854) was founder of the Izbica/Radzyn dynasty. He was a student of R. Simhah Bunim of Przysucha (Peshiskhan) and R. Menahem Mendel Morgenstern of Kotsk, and was considered the latter’s outstanding student. After the famous “Friday night incident” in 1839, which remains obscure, he left Kotsk, finally settling in Izbica, where he resided for thirteen years. The decisive year of his life was 1840, prophesied as the year of redemption by many Hasidim (the Tarnikim). According to his grandson, R. Gershon Henikh, “he [R. Mordecai Joseph] remained hidden in the Cave of Adullam for 13 years studying the Torah in secret... until the time when the word of God came” (Mei ha-Shillo’ah). He is considered by many the most original thinker of Hasidism. He opposed the isolation of the Kotsker, emphasizing that the zaddik was a spiritual guide rather than a miracle worker, and believed in informed faith, that God should be served with intelligence as well as devotion.

[על התורה, נביאים וכתובים וליקוטים]. לובלין, דפוס נחמה הערשענהארן ושלמה שמעון שטרייזבערגער, תרפ"ב. עו דף. דף ב-ג: הקדמת ר' מרדכי יוסף ב"ר יעקב ליינער, נכד המחבר, שסידר את הספר. חלק ב: דף עג-עו: הוספות לחלק [א].