Attorney-general Mohamed Apandi Ali must swear on the Quran that the Malaysian Anti-Corruption Commission (MACC) and Bank Negara had not implicated Prime Minister Najib Abdul Razak in graft, dared former prime minister Dr Mahathir Mohamad.

"As a good Muslim, he should swear on the Quran in a mosque witnessed by mosque officials and the public that the reports did not implicate Najib in any way.

"He should not try to cheat by vowing in his heart something else, and swearing aloud something else. That would be a double sin. He will go to a worse hell," Mahathir wrote in his blog today.

Three weeks ago, Apandi cleared Najib of any wrongdoing in the RM2.6 billion donation and RM42 million SRC International scandals.

He has ordered the MACC to stop pursuing the case unless it has new evidence.

Apandi had also decided that there would be no further action on Bank Negara's probe on 1MDB.

Najib has denied any wrongdoing in either scandal, and has dismissed allegations that he misused public funds as a conspiracy to topple him.

Mahathir ( photo ) said Apandi's dismissal of the MACC and Bank Negara probes has destroyed the AG's credibility.

He also said the top lawyer's plans to strengthen the Official Secrets Act to include life imprisonment for whistleblowers and journalists were suspicious.

"He proposes life imprisonment for leaking government information – a sure indication that he is hiding the truth," Mahathir said.

In his blog today, Mahathir also repeated his call for the Inland Revenue Board to probe the RM2.6 billion case, saying it was "obviously beyond what the prime minister of Malaysia can have".

He also called on the MACC to investigate if Najib's lifestyle was within his means as the premier.