Former South African president Jacob Zuma staged a walkout at the commission investigating corruption during his tenure after failing in his legal bid to get the panel’s chairman to step aside.
Zuma was set to take the witness stand after the ruling on Thursday, but he left despite appearing under a summons.
Seeking what he called an “impartial” judge, Zuma had accused Judge Raymond Zondo of bias and demanded he recuse himself.
But Zondo rejected the application, saying it “failed to meet the test for a reasonable apprehension of bias”.
“The application for my recusal falls … and it is accordingly dismissed,” ruled Zondo who is also deputy chief justice of South Africa’s Constitutional Court.
Zondo has headed the judicial inquiry commission since it was set up in early 2018, when Zuma was still in office.
But relations between the two men have been frosty over the past year.
Zuma’s lawyer Muzi Sikhakhane accused Zondo of having become “a judge in a dispute that involves yourself”.
Sikhakhane requested that proceedings be suspended so that he could review the judgement.
The former president’s legal steps against the commission and its chairman are widely seen as delaying tactics to avoid facing questions about his role in alleged corruption that occurred largely from 2009 to 2018.
Zuma was summoned to respond to questions related to evidence contained in at least 34 affidavits submitted to the commission. Lavish government contracts were awarded to an Indian business family, the Guptas, among other scandals.
Zuma this week appeared before the commission for the first time in more than a year after abandoning his testimony in 2019.
The ex-president pulled out after a few days, saying he was being treated as an “accused” rather than as a witness.
Since then he has not testified again, citing health concerns or his preparation for another corruption case related to a 1990s arms deal.
The ruling African National Congress (ANC) forced Zuma to step down in 2018, and his successor Cyril Ramaphosa has promised to tackle corruption.
The largest opposition Democratic Alliance party slammed Zuma’s “spurious” bid as aimed at derailing the work of the commission that has so far cost the South African taxpayer more than 700 million rand ($45 million).