A document purporting to be a copy of their application for a birth certificate for Thandekile Matina Zuma has the answer "yes" in reply to the question: "Are the parents of the child married to each other."
The document appeared to have been signed by Zuma and Khoza.
Under "Nature of Marriage" the option "customary" was checked.
An official of the department of home affairs said that the document - faxed anonymously to The Times yesterday morning - appeared to be valid, but neither Zuma's spokesman nor Khoza would confirm that this was so.
Cellphone numbers, addresses and ID numbers on the document match those of Zuma and Khoza.
Zuma is listed as the "natural father" of Khoza's four-month-old daughter, who was born in Johannesburg on October 8.
The section marked "Acknowledgement of paternity [in respect of] a child born out of wedlock" is signed by JG Zuma in the box marked: "I hereby declare that I am the natural father of the above child."
The document is date stamped January 19, two days after Zuma's motorcade reportedly arrived at the Khoza family's mansion in Diepkloof Extension, Soweto.
It was also signed by an official at the Home Affairs office in Randburg.
The Sunday Times reported that two men from KwaZulu-Natal, acting on Zuma's behalf, visited the Khoza family in December to discuss the Zulu customary damages, inhlawulo, due when a child is born out of wedlock.
Yesterday, the 39-year-old daughter of soccer boss Irvin Khoza refused to comment on the document.
"I am shocked, sjoe, that is all I can say. I have told you guys that I have nothing to say. How can I confirm things that have been done by other faceless people. I have nothing else to say," she said.
The bank executive did not, however, deny the birth or that marriage rites had been completed.
The Times reported yesterday that a neighbour, who described herself as a close family friend of Khoza's wife, Matina, said the community knew about Zuma and Sonono's relationship "from the word go".
"They will get married, they are in love with each other ... what is wrong with it? It's official - they will get married."
The woman said she had recently discussed the relationship with Matina Khoza.
When The Times telephoned Matina Khoza and asked her about the document last night, she replied: "It does not concern you." She then hung up.
The Times also e-mailed a copy of the document to Zuma's ANC spokesman, Zizi Kodwa, who promised to respond within 30 minutes. But by the time of going to press, Kodwa had not responded, despite numerous attempts to contact him.
The document was also sent to presidential spokesman Vincent Magwenya, who was boarding a plane to return from Ethiopia, where Zuma had attended an African Union summit.
He also did not respond.
Another presidential spokesman, Vusi Mona, said he could not respond because he was attending a conference in London.
If Khoza is indeed Zuma's customary wife, this would bring to four the number of women married to the president.
He is also engaged to be married to Bongekile Gloria Ngema, for whom he paid lobolo late last year.
The storm over the Khoza liaison continued yesterday with opposition parties slamming the ANC for its earlier attempts to justify the president's behaviour.
But the SA Students' Congress, which has its head office at the ANC's Luthuli House HQ - slammed the media for reporting on the birth of Zuma's latest child.
Sasco president Mbulelo Mandlana told reporters in Johannesburg yesterday that the media had "no respect for the elderly".
"We view these reports as part of the anti-Zuma campaign by newspapers."
BabyMama