James Comey, the former FBI director who was fired by President Trump last month, is expected to tell a Senate committee that the president asked him to back off the investigation into Mike Flynn, a source told The Wall Street Journal on Wednesday.

The report said Comey could testify as early as next week.

The New York Times first reported that Comey in February wrote a memo that Trump had asked him to shut down the investigation into Flynn, the former national security adviser. The memo's existence was confirmed by Fox News.

The memo reportedly said that Trump said to Comey that, “I hope you can let this go.” The president reportedly was referring to Comey’s FBI’s investigation into Flynn.

Flynn was forced to resign Feb. 13, the day before the conversation between Trump and Comey depicted in the memo.

A Comey associate, who wasn’t authorized to discuss details of the testimony, told The Associated Press that Robert Mueller III, who was appointed earlier this month by the Department of Justice to lead the government’s inquiry, is allowing Comey to make certain statements.

A spokesman for Mueller responded to Fox News’ request for comment, but said he did not have any information on Comey’s potential testimony, or whether Mueller has cleared the former FBI director for public testimony.

Congress is currently out of session. It resumes next Tuesday. No date for testimony in front of the intelligence committee has been set.

“The committee welcomes the testimony of former Director Comey, but does not have an announcement to make at this time,” a Senate Intelligence Committee spokeswoman told Fox News on Wednesday.

The House panel pursuing its own investigation of the Trump campaign and possible Russia ties also has sought information from Comey, asking the FBI to turn over documents related to his interactions with both the White House and the Justice Department.

Trump has repeatedly dismissed allegations that his campaign collaborated with Russia ahead of the presidential election. Early Wednesday morning, the president tweeted “Witch Hunt!” in reference to testimony by Comey and former CIA Director John Brennan before Congress on the topic.

But later in the day, the White House showed it was beginning to offload the Russia crisis to Trump’s longtime personal attorney, Marc Kasowitz.

At a Wednesday briefing, press secretary Sean Spicer refused to answer a reporter’s questions about developments in the probe, saying all such inquiries must be directed to Trump’s outside counsel. It marked the first time the White House officially acknowledged that outside counsel had been retained.

Fox News’ Brooke Singman contributed to this report.

The Associated Press contributed to this report.