Bill Gross, manager of the world’s largest mutual fund, said fellow billionaire investors Carl Icahn should stop pushing Apple Inc. for additional share buybacks.

“Icahn should leave Apple alone and spend more time like Bill Gates,” Gross, who runs the $250 billion Pimco Total Return Fund at Pacific Investment Management Co. in Newport Beach, California, wrote in a message on Twitter. “If Icahn’s so smart, use it to help people not yourself.”

Icahn, who has taken stakes and agitated for stockholder friendly changes at companies from Dell Inc. to Transocean Ltd., said in a Bloomberg Television interview with Trish Regan that Apple should buy back $150 billion of shares and criticized the board isn’t acting to enhance value.

Icahn, in a letter to Apple Chief Executive Officer Tim Cook, said he increased his holding in the company to 4.7 million shares worth $2.5 billion from 3.4 million shares in August, and added that he intends to buy more of the stock that he said is undervalued.

Icahn is ranked 34th on the Bloomberg Billionaires Index of the world’s richest people, with a net worth of $21 billion. In 2012, he pledged $200 million to the Mount Sinai School of Medicine, the biggest donation ever given to the New York City teaching hospital. He’s also endowed five charter schools in the city and has pledged to give the majority of his wealth to charity.

Gross’ personal wealth is estimated at $2 billion. He has endowed a foundation with $293 million in assets and raised money for Doctors Without Borders, a medical charity, by selling parts of his stamp collection.

Mark Porterfield, a spokesman for Pimco, confirmed the Twitter message was posted by Gross. Icahn didn’t immediately respond to a phone message left with his office.