Prime Minister Dr Mahathir Mohamad has challenged Najib Abdul Razak to furnish evidence that one of his aides had collected RM10 million in cash from the latter's residence before the 2013 general election.

"Show evidence, ask him to show evidence," he said after opening the American Chamber of Commerce annual general meeting luncheon in Kuala Lumpur today.

In an exclusive interview with Malaysiakini yesterday, Najib, in explaining why he kept cash for BN's campaign expenses, had alleged that "one of Mahathir's people" had collected RM10 million in cash from him for the 13th general election (GE13).

During GE13, Mahathir had yet to part ways with Umno with his son Mukhriz winning the Ayer Hitam state seat in Kedah. Mukhriz went on to become Kedah menteri besar after BN won the state.

Najib had named the aide in question, who is a well-known swimmer, but Malaysiakini is withholding his identity pending his response to the news portal's request for comments.

Yesterday, the former premier had also said the jewellery and valuables seized from residences linked to him were “gifts” he accumulated in his four decades in politics.

This was something Mahathir had practised as well, he said.

“But what I do know is that over the years as head of the government, we have been gifted with a lot of items by foreign leaders as well as personal friends, and I do know that under the law it is not illegal to receive gifts. These gifts were accumulated over decades," he said.

“For example, (Prime Minister) Dr Mahathir (Mohamad) admitted to receiving 40 horses from his friends and foreign leaders, and he openly uses a lot of corporate jets from his friends, so it is not illegal to receive gifts,” Najib had said.

According to the police, the market value of all luxury items seized from Najib’s house and properties linked to him amount to RM1.1 billion.