Former premier Dr Mahathir Mohamad said he had doubts about the source of Deputy Prime Minister Ahmad Zahid Hamidi's wealth when the latter declared his assets to him more than two decades ago.

However, Mahathir said he had no evidence.

"At the time he only made a verbal report to me, but I did not take the matter seriously. He (Zahid) explained it (the money) was supposedly income from businesses...