The whistle-blower told Mr Cummings that he was attending an inaugural event on Jan 20, where he met one of Flynn's key allies on this project, Mr Alex Copson, who is described as a managing partner of ACU Strategic Partners, and was working with Flynn to promote the joint project with Russian Federation to build nuclear reactors in the Arab world.
Cummings did not identify the witness, whom he described as a whistleblower.
President Trump's personal White House lawyer, Ty Cobb, also declined to comment.
The Trump administration did not roll back the sanctions. Congress later passed a bipartisan measure that placed new sanctions on Russian Federation, a bill that Trump reluctantly signed in August.
That's the explosive, but unverified, allegation of a whistleblower cooperating with House Democrats probing the myriad scandals surrounding Flynn, who pleaded guilty earlier this month to lying to the Federal Bureau of Investigation about his contacts with a senior Russian diplomat.
The congressman said the informant had met Mr Copson at an inaugural event in Washington DC on 20 January.
Mr Copson explained that Flynn was making sure that sanctions were going to be "ripped up" as one of the first orders of business and this would allow money to start flowing to the project.More news: Sensex slips 108 pts ahead of RBI meet, on Asian cues
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During their conversation, Mr. Copson informed the whistleblower that he "just got this text message" from General Flynn that the project was "good to go" and directing Mr. Copson to contact their business colleagues to "let them know to put things in place".
According to the whistleblower account, Copson said the inauguration was "the best day of my life" owing to progress on the nuclear deal, which was now 'going to make a lot of very wealthy people.
Copson showed the witness the text on his phone. The whistleblower saw that the time stamp of the message was 12:11 pm, but did not read the text.
Neither Copson nor an attorney for ACU responded to a request for comment.
"Although this individual was extremely hesitant to come forward - and still fears retaliation - the whistleblower has chose to do so now because this individual feels duty bound as a citizen to make this disclosure", he wrote.
Perhaps most intriguingly of all, Cummingswrites that he told Special Counsel Robert Mueller's team about all this some time ago - and that they asked him to delay publicly revealing this information "until they completed certain investigation steps". Mr. Copson confirmed in a letter to me on June 27, 2017, that his company paid the expenses for a trip General Flynn made to the Middle East in June 2015 to promote his project and provided a $25,000 check to compensate him for the "loss of income and business opportunities resulting from this trip".
The whistleblower also said that within minutes of Trump's inauguration ceremony, Flynn communicated directly with business associates about plans to begin building nuclear reactors in the Middle East-a joint project with Russian Federation, according to the letter.