A quick Google search isn't returning much, but it's hard to find a good set of terms to search for. I recall spending a lot of time in a class talking about it, though. At once point we were given quotes and asked to identify them as being either MLK or MX, and, not surprisingly in this context, all of the quotes about avoiding violence were from Malcolm X, and all of the ones demanding violent revolution were Martin Luther King.
I don't doubt the memory just because there's nothing more dangerous than a teacher who can't recognize a Bible quote and who then attributes modern meaning to the speaker. MLK was a reverend so he obviously quoted the Bible a lot and the Bible can have some violent imagery.
But I can't see the man who said this advocating violence of any kind...
"Nonviolence is the answer to the crucial political and moral questions of our time: the need for man to overcome oppression and violence without resorting to oppression and violence. Man must evolve for all human conflict a method which rejects revenge, aggression and retaliation. The foundation of such a method is love."