My Friend has been saying things about my other friend behind her back.

My group of friends have always been a trio. My friends are H, M, and the new girl is D. Lately D has been joining in our group for some time now. But H doesn't like her because D doesn't like H. The other day D was hanging out with me and M, and D was saying how she doesn't like H because she was is an annoying b*tch, Then M said "Yeah, she is annoying and a b*tch." Then when D had left, M looked at me and said not to tell H what she herself (M) had said. So when I caught the bus with H, I told her what D had said. Later that night, M started abusing me saying I shouldn't have said anything at all even though she said nothing to me about not telling H what D had said. Should I have told H, said nothing or what? Please Help Me, I don't want my friends to be angry at me or anything.