Officials from the National Museum of African American History and Culture approached the leaders of the historic Alfred Street Baptist Church in Alexandria with a surprising request: Would the African American congregation pledge $1 million to become a founding donor to the $540 million museum, opening Sept. 24 next to the Washington Monument on the Mall?

The gift would be historic, museum officials said, representing the largest donation by a faith-based organization. It would be groundbreaking for the congregation, too, which had never given that much to another institution.