CNN appears to have regurgitated the WaPo article with the addition of running a Wikipedia search and demanding answers from the White House on this issue of national import:

CNN - Oval Office rug wrongly attributes quote to MLK

photo caption - A quote on the perimeter of the new presidential rug in the Oval Office is wrongly attributed to Martin Luther King, Jr. (PHOTO CREDIT: Shawna Shepherd/POOL)
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While the origins of Parker’s proclamation are rarely cited in today’s public discourse, a search on even the most basic of research tools, Wikipedia, reveals Parker as the voice behind the words.

White House Deputy Press Secretary Bill Burton on Saturday stood by the quote on the rug, noting that Martin Luther King Jr. did utter precisely the same words on September 2, 1957. Burton said that Theodore Parker’s quote is slightly different.