Chelek 34, Voeschanan 1

From The Sicha, Rabbi Chaim Wolosow by R Chaim Wolosow.

Why Rabbi Zeira Sought to Forget the Babylonian Talmud

Why was Rabbi Zeira permitted to fast in order to forget the Babylonian Talmud? The Alter Rebbe explains that forgetting Torah is forbidden because it separates a person from Torah. Rabbi Zeira's goal, however, was the opposite—to attain a deeper and more enduring attachment to Torah through the Jerusalem Talmud.