The Democratic Party nominee for president was discussing false rumors on ABC's "This Week with George Stephanopoulos" when he made the gaffe, the Sun-Times reported Monday.
Obama suggested that GOP rival Sen. John McCain was behind false rumors that he is a Muslim. Stephanopoulos then reminded him that McCain denied spreading the rumors.
"You're absolutely right that John McCain has not talked about my Muslim faith," Obama said before Stephanopoulos corrected him.
The Sun-Times says the verbal slip unleashed a barrage of Internet attacks, becoming a magnet for comments on the YouTube.com video site.
"Printing a blogger suspecting that Obama is a Muslim is pretty irresponsible and below the standards that we're used to out of the Sun-Times," Obama spokesman Bill Burton wrote in an e-mail message to the newspaper.