Prime Minister Najib Abdul Razak and his supporters should stop thinking Malaysians are stupid, said Dr Mahathir Mohamad.
In a blog posting today, the former premier urged them to cease attempts to convince Malaysians that the RM2.6 billion in Najib's private accounts is a donation.
"The public has a right to know because the public does not believe the RM2.6 billion was a gift personally to the PM of Malaysia for him to win elections.
"Malaysians would not like to believe their candidate for the highest office in the country is a nominee of some person from another country.
"What will be his obligation to his supporters? Will he serve Malaysians or some foreign country?" he added.
Mahathir reiterated his claim nobody believes such a huge sum could be donated to Najib for whatever reason.
"Explaining that it was given because of Malaysia's stand against the Islamic State is absurd as the Islamic State showed their brand of terrorism only in 2014 whereas the money came in 2013 or before.
"Saying it is because of Malaysia's moderation in Islam is equally absurd as Malaysia had never been extreme in its practice of Islam," he added.
Questioning the need for RM2.6 billion, the former premier argued the amount was too large for the needs of Malaysian elections.
"Except if it is to bribe the Malaysian electorate.
"Why should anyone want to bribe the Malaysian electorate so Najib would win?
"Malaysians have supported BN without the need to be paid huge bribes by anyone, least of all by foreigners," he added.
The official stand for the RM2.6 billion issue is that the sum was donated by a Middle Eastern source.
The Malaysian Anti-Corruption Commission also confirmed this, but declined to reveal the identity of the donor.
However, it is still probing the issue.