I knew it was by a German theologian, but I guessed the wrong one. It was a quote from Martin Niemöller (1892-1984). Don't know the original source, but it was published in the U.S. Congressional Record 14 October 1968:

When Hitler attacked the Jews I was not a Jew, therefore, I was not concerned.
And when Hitler attacked the Catholics, I was not a Catholic, and therefore, I was not concerned.
And when Hitler attacked the unions and the industrialists, I was not a member of the unions and I was not concerned.
Then Hitler attacked me and the Protestant church - and there was nobody left to be concerned.

often quoted in the form "In Germany they came first for the Communists, and I didn't speak up because I wasn't a communist..." and so on
Source: Oxford Dictionary of Quotations

-Joe Offer-