Mnangagwa said this when the two men spoke for the first time since he returned home this week, according to the state-owned The Herald newspaper.
Mugabe and Mnangagwa had reportedly agreed that the former leader may not attend the swearing-in ceremony because he was tired.
But there is no immunity for Mugabe’s former aides detained last week by the military in an operation against “criminals” around the ousted president.
Former finance minister Ignatius Chombo, who was among those arrested, has been handed over to the police, a relative said on Friday.
The unnamed relative said Chombo had been severely beaten while in military custody, Reuters reports.
Police spokeswoman Charity Charamba said she had no information about Chombo.