PKR president Anwar Ibrahim wants authorities to probe allegations that preacher Wan Ji Wan Hussin was assaulted during his brief detention at Kajang prison.
"I believe Wan Ji is a credible person who won't make things up.
"So, it is appropriate (that it is investigated) - in this case, it is Kajang prison which should investigate and I believe the home minister will take action to ensure an investigation," he told journalists at the Parliament lobby.
Last Sunday, Wan Ji alleged he was assaulted by a warden while other wardens watched and laughed.
"There was one person who spoke in Kelantanese dialect. He had his face covered and was wearing a warden's uniform.
"He asked for my name. I said 'Wan Ji'. He then asked me to take off my glasses and then 'bam, bam', he gave it to me three times," he had said.
Wan Ji was sent to prison by the Shah Alam High Court judge Abdul Halim Aman on July 9, despite the defence indicating that they planned to appeal and wanted a stay on his enhanced one-year sentence under the Sedition Act 1948.
He was released on July 12 after his lawyers formally filed a stay on the sentence.