With Selma and the voting rights bill one era of our struggle came to a close and a new era came into being. Now our struggle is for genuine equality, which means economic equality. For we know that it isn’t enough to integrate lunch counters. What does it profit a man to be able to eat at an integrated lunch counter if he doesn’t earn enough money to buy a hamburger and a coup of coffee?

Martin Luther King, Jr. (1929-1968) American clergyman, civil rights leader, social activist, preacher

Speech to Striking Sanitation Workers, Memphis, Tennessee (18 Mar 1968)

King appears to have used the phrase on a number of occasions (I found references to a Birmingham sit-in and to 1965), but the above is the one case, a few weeks before his death, that I was able to pin down.

Other (earlier) versions one finds quoted and paraphrased:

• "It does no good to be able to eat at a lunch counter if you can't afford to buy a hamburger."
• "It doesn't do much good when you can sit at a lunch couner but you can't afford to buy a hamburger."
• "What good does it do to be able to eat at a lunch counter if you can't buy a hamburger?"