Shemirat HaLashon
(Bereshith 9:22): "And he [Cham] told his two brother outside": The Torah hereby tells us his sin, that aside from not covering him [Noach] himself, he also told of it outside; that is, in the market, as Onkelos says, paying no heed to his [Noach's] state, not to shame him before people — wherefore he [Noach] cursed him.