Mandela, 94, was admitted to the hospital Wednesday for treatment of a lung infection. He was comfortable after a procedure to drain fluid from his lungs, presidential spokesman Mac Maharaj said Saturday.
"Doctors advised that due to the lung infection, former President Mandela had developed a pleural effusion which was tapped. This has resulted in him now being able to breathe without difficulty," he said.
"He continues to respond to treatment and is comfortable."
Several hundred people gathered to pray at the Regina Mundi church in Soweto, a major focal point of the struggle against apartheid, the BBC reported.
Mandela's lungs may have been damaged while working in a prison quarry during nearly four decades of imprisonment, the BBC reported. He was freed from prison in 1990 and served as the country's first black president from 1994 to 1999.
The hospitalization is Mandela's fourth in just over two years.