On March 31, 2014 then ANC treasurer-general Zweli Mkhize thanked Bosasa CEO Gavin Watson for a R3m donation to the governing party, less than two months before the national and provincial elections in that year.
"Dear Mr Watson," Mkhize wrote on an official ANC letterhead, "This serves to acknowledge the receipt of R3,000,000.00 (Three Million Rand) donation to the AFRICAN NATIONAL CONGRESS.
"On behalf of the African National Congress, I would like to express our sincere appreciation and gratitude to your organisation for this donation and for the continued financial support and contribution your organisation renders to the ANC.
"Your ongoing support for our organisation is appreciated."
News24 previously reported on a picture showing Watson and his colleagues with Mkhize after handing over money to the party at Luthuli House.
On Thursday, DA leader Mmusi Maimane handed a copy of Mkhize's letter to President Cyril Ramaphosa in Parliament, asking him what Mkhize meant by the "continued financial support" from Bosasa.
By 2014, corruption allegations against Bosasa had been in the news for several years. In 2009, the National Prosecuting Authority announced that it had received a report into corruption between Bosasa and the department of correctional services and handed it to the Hawks for further investigation.
Former Bosasa chief operations officer Angelo Agrizzi told the Zondo Commission that the company had supported the ANC financially for many years. News24 reported that according to a company insider, Bosasa donated at least R40m to the ANC over the years.
The company's campus in Krugersdorp was used as a "war room" by the ANC during the 2014 and 2016 elections.
Ramaphosa said he would study the letter and respond to Maimane later.
Public Protector Busisiwe Mkhwebane ruled last month that Ramaphosa had contravened his oath of office when he "deliberately misled" Parliament over a R500 000 donation to his campaign for the ANC presidency.
Ramaphosa has taken Mkhwebane's report on judicial review.