The whistleblower said he noted the time stamp, but did not read the text.
Reached Wednesday, Flynn’s attorney declined to comment.
The new account offers a window into the range of allegations being shared with the FBI as agents prepared to negotiate a cooperation agreement with Flynn. Flynn’s consulting firm, the Flynn Intel Group, had numerous clients exploring business ventures that would require some involvement from federal government agencies.
The whistleblower told congressional investigators he was with Alex Copson, a former business associate of Flynn’s, watching the Trump inauguration ceremony at an event in Washington, according to the letter. The whistleblower alleged Copson showed off the text to those around him, calling it “the best day of my life.”
Copson allegedly told those around him that “Mike [Flynn] has been putting everything in place for us. This is going to make for a lot of very wealthy people,” Cummings’s letter quotes him as saying.
The whistleblower told congressional investigators that Copson boasted that Flynn was “making sure that sanctions would be ‘ripped up’ as one of his first orders of business and that this would allow money to start flowing into the project,” an apparent reference to financial sanctions imposed on Russia by the Obama administration, Cummings’s letter states.
Copson, who worked at the firm ACU Strategic Partners, refuted the whistleblower’s assertion in a statement to ABC News from his lawyer, Donald Gross.
“For the record, no member of ACU received any communication in any form from General Flynn during the presidential campaign, the presidential transition, the Inauguration, the period following the Inauguration when General Flynn served as national security adviser or subsequent to General Flynn's resignation,” the statement said.
House investigators turned over the information they had gathered to the Mueller team several weeks ago. Prosecutors “asked my office to hold on the public release of this information until they completed certain investigative steps,” Cummings wrote. “They have now informed us that they have done so.”
Gowdy has pressed back previously on the demands for records, saying he does not want to impede the Special Counsel investigation.
Gowdy responded to Cummings’s letter late Wednesday, saying he did not believe the matter was in the jurisdiction of the House Oversight committee, but rather should be handled by the House Intelligence committee or the Special Counsel.
“What you allege here is a crime, squarely within the jurisdiction of the Special Counsel,” Gowdy wrote. “If you have evidence of a crime, you should provide it to the Special Counsel immediately.”
Cummings has argued that the Flynn plea deal should alleviate that concern. Cummings said he believes Republican leaders of the Oversight Committee should approve a subpoena so they can “pursue these allegations against General Flynn in a responsible way.”
The whistleblower is not named in the five-page letter that Cummings shared with ABC News on Wednesday, and is unlikely to identify him or herself, fearing retaliation. “I have spoken to this whistleblower, and I find this person to be authentic, credible, and reliable,” Cummings wrote.