The commission said the money was not from 1Malaysia Development Berhad (1MDB),a state investment fund headed by Mr Najib that is $US11 billion in debt and the subject of several investigations in Kuala Lumpur.
Earlier the fund denied transferring money to the Prime Minister.
Mr Najib has threatened to sue the Wall Street Journal over a July 2 report that claimed Malaysian investigators had traced almost $US700 million of deposits into what investigators believed were Mr Najib's personal bank accounts after the movement of cash among agencies,banks and companies linked to the fund.
The newspaper reported that the original source of the money was unclear.
Mr Najib,who has denied taking any money for personal gain,made no comment on the commission's statement.