and here’s an alternative link for if you’re on mobile and find the design of that page miserable to read. (note that the transcript is slightly different, as it records a different performance of the speech than that in the link provided by the esteemed other commenter.) https://www.crmvet.org/docs/otheram.htm

you’re referring to a book called The Other America. This post, and the quote in it, is from a speech by the same name, given by MLK in '68