The deal, worth more than US$1.8 billion at list prices, is expected to be one of the announcements that will be made after Najib meets with US President Donald Trump on Tuesday, the sources said.
Najib is scheduled to witness a memorandum of understanding signing ceremony between Malaysia Airlines and Boeing, according to a schedule of the Prime Minister's events in Washington reported by Malaysian media outlets.
Malaysia Airlines said it would not comment on reports that are speculative in nature. The sources did not want to be named because the discussions were private.
The airline's chief executive said in June that it was in early negotiations with Airbus and Boeing for the purchase of 35-40 new long-range jets.
Aircraft manufacturers typically give discounts to list prices.
Boeing and Airbus declined to comment. - Reuters