Reuters’ Jennifer Coogan writes about the market taking a tumble after CNBC’s Charles Gasparino made a comment. (via Talking Biz News)

On Wednesday, the three major U.S. benchmark indexes had each been up by more than 1 percent after the Federal Reserve cut the fed funds rate by a half percentage point at 2:15 p.m.

Then, shares of Ambac and MBI tumbled abruptly at around 3:10 p.m. when CNBC On-Air-Editor Charles Gasparino made his comments about the companies. Major indexes quickly followed suit.

“My gut is telling me Moody’s and S&P are going to downgrade either one or both,” Gasparino said on air. CNBC later posted a report on its Web site saying the network had learned that the downgrade could come as early as Wednesday. The report cited no sources for the information.

Traders attributed the market’s about face to the Gasparino report, noting the S&P 500 slid rapidly from its session high, reached at about 3:08 p.m.

“Once he started talking, we got the sell-off,” said Joe Saluzzi, co-manager of trading at Themis Trading in Chatham, New Jersey. “Any time (Ambac and MBIA) go down, they take the entire market with them.”