In 1924 (or 1925[1]), in response to a call from the Ger Rebbe, Rabbi Avraham Mordechai Alter, Kasher moved to Jerusalem, in Mandate Palestine, to establish the Sfas Emes Yeshiva in honour of the Rebbe's father, Yehudah Aryeh Leib Alter. He subsequently served as the rosh yeshiva of the yeshiva for its first two years. He later helped bring the Rebbe to Palestine about six months after the outbreak of World War II.