As far as I know he ever advocated for it, but he understood it as an inevitable reaction.
Off the tip of my head the only specific quote I can think of is his
"I think that we’ve got to see that a riot is the language of the unheard. And, what is it that America has failed to hear? It has failed to hear that the economic plight of the Negro poor has worsened over the last few years.”
Between this and the US military maybe being deployed in LA tonight...we are in for a wild ride in the coming days.