Then-incoming national security adviser Michael Flynn also allegedly texted a business partner that a nuclear power project with Russians was "good to go".
But he asked Gowdy to issue a subpoena to the White House for documents related to Flynn, saying that the committee has "credible allegations" that Flynn "sought to manipulate the course of worldwide nuclear policy for the financial gain of his former business partners".
On Wednesday Cummings sent the whistleblower's account to committee chairman Trey Gowdy with a request that he issue subpoenas to White House officials, including chief of staff John Kelly, as well as Flynn, Copson and their other business associates for material that would corroborate the whistleblower's statements.
But in his interview with the Federal Bureau of Investigation last January, 24, according to the Justice Department documents, Flynn lied when he said he did not ask Kislyak "to refrain from escalating the situation in response to sanctions that the United States had imposed against Russian Federation".
The whistleblower told House Democrats that while Trump spoke at his inauguration, Flynn texted from his seat on the Capitol steps to Alex Copson, the managing director of ACU Strategic Partners and the nuclear project's main promoter.
It is alleged that while sitting a few yards away from the podium where President Trump was delivering his inaugural address on 20 January, Mr Flynn sent the texts to Alex Copson, managing partner of ACU Strategic Partners, a United States nuclear power consultancy.More news: Director Bryan Singer fired from upcoming Queen biopic
The office of special counsel Robert S. Mueller III was aware of the witness's account and asked Cummings not to release the information until the special counsel had taken "certain investigative steps", which are now complete, Cummings wrote. The Wall Street Journal reported in September that despite records showing Flynn's work on the project ended in December 2016, Flynn continued promoting the plan to colleagues inside the White House.
After getting the texts, Copson said, "Mike has been putting everything in place for us", and, "This is going to make a lot of very wealthy people", Cummings said, quoting the witness.
"This is the best day of my life", Copson told the whistleblower as he described the message from Flynn, Cummings said.
Flynn, while involved in the Trump transition, worked with companies including ACU Strategic Partners to make a deal with Russian Federation to build nuclear reactors in the Middle East. He and Cummings jointly exposed details that Flynn had lied on his security clearance forms earlier this year, though Chaffetz later backed off the inquiry despite the Democratic demands.
Media captionAfter Flynn's guilty plea, what next for the Russian Federation investigation?
Flynn's attorney did not immediately respond to a request for comment. He said Flynn did not cash the check, however.
Cummings said the whistleblower, whom he did not identify in the letter, "fears retaliation", but would speak with Gowdy if he agrees to protect the whistleblower's identity.