She said Trump has not decided which organization he will donate to. The spokeswoman said Trump specifically told Sanders to ask journalists at the briefing for suggestions since they have been reporting on groups and their relief efforts.
"As I said, he'll pledge proudly $1 million of his own personal money to help the people of both Texas and Louisiana," Sanders said.
Trump donated his first two quarters' worth of presidential pay to government agencies. He gave his first installment to the National Park Service and his second to the Department of Education.
Trump and first lady Melania Trump will travel to Texas and Louisiana on Saturday, Sanders said. The two visited Corpus Christi, Texas, on Tuesday. Vice President Mike Pence toured damage in Rockport, Texas, on Thursday.
The details of the Trumps' next trip are still being finalized, Sanders said. The tentative plan is for the first couple to travel to Houston, Texas, and Lake Charles, Louisiana, she said.
Once he makes the donation, Trump will join a long list of donors who have promised at least $1 million to relief efforts. The Abbvie Foundation has committed $1 million in funding. The Allstate Foundation has pledged $1.55 million to relief and is matching employee and agency owner contributions.
Vizient has announced a $1 million donation raised from the company and employees to help hospital workers. Houston-based Reliant donated more than $2 million for relief efforts.
J.J. Watt, star defensive lineman for the Houston Texans, has raised $10 million.
Correction: This story was updated to reflect Sanders' quote that Trump proudly pledged a donation.