Musar do Kapłańska 13:59

And what need is there for me to elaborate on the greatness of this sin, when they have already said that he [a speaker of lashon hara] is like one who transgresses the five books of the Torah and a denier of the Deity, G-d forbid. For this is the language of the Midrash Rabbah (16:1): "R. Yehoshua b. Levi said: Five "toroth" are written in the parshah: (Vayikra 13:59): "This is the Torah of the plague-spot of leprosy"; (Ibid. 14:54): "This is the Torah for all plague-spots of leprosy"; (Ibid. 14:2): "This shall be the Torah of the leper"; (Ibid. 14:32): This is the Torah for him with a plague-spot of leprosy"; (Ibid. 14:57): "This is the Torah of leprosy" ["hametzora," (acronym for)] "hamotzi shem ra," ("one who spreads a false report") — to teach you that one who speaks lashon hara transgresses five books of Torah.