"Some are even saying the president is a witch, how many did I kill? We have travelled a long journey together and why kill today?"
The veteran leader said that it was normal for people to fall sick, including those in top leadership.
Mugabe said this while speaking at the burial of two Zanu-PF stalwarts over the weekend.
He lashed out at Masvingo politicians for claiming Mnangagwa was poisoned or bewitched.
"This is not the Masvingo tradition that we know... So if you have your witch doctors who are telling you about being bewitched, down with your witchcraft issues," Mugabe was quoted as saying.
However, the nonagenarian's detractors accused him of double standards since he also accused his former deputy president Joice Mujuru of witchcraft.
Mnangagwa was flown to South Africa for emergency medical care two weeks ago after he started vomiting and had severe diarrhoea.
The deputy president, who was seen as a favourite to succeed Mugabe, fell ill at a rally where the president was speaking on August 12.