Abudrahman Alamoudi, of the American Muslim Council, made his donation to Clinton's Senate campaign in May.
"We are the ones who went to the White House and defended what is called Hamas," Alamoudi once boasted, the Daily News reported Wednesday. Members of the council have visited the White House to celebrate Muslim holidays.
U.S. officials have labeled Hamas a terrorist organization because it has taken responsibility for numerous suicide bombings on Israeli civilians.
A council representative told The Associated Press on Wednesday that Alamoudi was out of the country and couldn't be reached for comment. The representative declined further comment.
Alamoudi also gave $1,000 to Gov. George W. Bush's presidential campaign in May, according to a database maintained by the Federal Elections Commission, which documents campaign donations. A call placed to Bush's headquarters in Texas for comment was not immediately returned.
The Clinton campaign learned of Alamoudi's support for Hamas on Tuesday and returned his contribution immediately, Clinton spokesman Howard Wolfson said.
"Hillary is a strong supporter of peace and security for Israel," he said. Jewish support is crucial for Clinton in her Senate race against Republican Rep. Rick Lazio. Jews accounted for about 12 percent of voters in New York's last general election. Polls have shown Clinton leading Lazio by a 2-to-1 ratio among Jews and 50 percent to 43 percent overall.
Also Wednesday, the News reported that the American Muslim Alliance, whose leader supports the Palestinians' right to use armed force against Israel, collected $50,000 for Clinton's Senate campaign on June 13 at a $500-a-ticket Boston fund-raiser. The group said Clinton was presented with a plaque honoring her human rights efforts.
Clinton's campaign confirms she attended the event but claims the alliance was not the sponsor. The event was sponsored by Boston-area Muslims, and the alliance was not mentioned in the invitations, Clinton campaign officials said. The plaque, however, is inscribed as being given by the alliance, the News reported.
"Someone who was at the event just handed her a plaque," Wolfson, the Clinton spokesman, stated bluntly. "The American Muslim Alliance did not host the event and did not raise $50,000."
The national president of the American Muslim Alliance, Agha Saeed, said Palestinians should pursue their own state in the West Bank and Gaza first through peaceful means. But he added that U.N. resolutions "say specifically they have the right to resist by armed force."