Dr Mahathir Mohamad attempted to outshine DAP with his remarks about Najib Abdul Razak and Prophet Muhammad, said Rizal Mansor, an aide to the prime minister's wife Rosmah Mansor.

"When he is with DAP, he has to show he is more DAP than DAP until he is willing to belittle his own prophet," he added in a media statement.

Rizal was responding to the former premier's speech at the DAP convention over the weekend.

Mahathir had said unlike Najib, Prophet Muhammad did not have RM2.6 billion in his accounts or 1MDB.

The former premier was referring to the RM2.6 billion in Najib's bank accounts, and the troubled state investment fund 1MDB.

Najib has denied abusing public funds for personal gain and accused Mahathir, who insists that the prime minister is embroiled in corruption, of attempting to topple him from power.

Attorney-general Mohamed Apandi Ali has cleared the prime minister of any wrongdoing and the RM2.6 billion is described as a donation from a Saudi royalty.

Meanwhile, Rizal said Mahathir’s remarks did not come as a surprise.

"Belittling the prophet is nothing new for Mahathir," he alleged.

He claimed that in 1997, Mahathir insulted Prophet Muhammad's beard, questioning if anyone had seen it and stating that there were no Gillette razors during that time.

Rizal further claimed that such remarks had cost BN the Arau seat in a 1998 by-election.