That's according to Reuters, which refers to an email from investor Whitney Tilson, investor Whitney Tilson, who is on the advisory board of Ackman's charity, Pershing Square Foundation, to his friends and professional contacts, Ukrinform reports.
"I had breakfast with my college buddy Bill Ackman this morning, walked him through the attached slide deck I put together about my ambulances-for-Ukraine mission, and on the spot he agreed to donate $3.25 million," Tilson wrote in the email, dated February 25.
Tilson has been leading an effort to buy ambulances for Ukraine that will be operated by humanitarian aid group MOAS (Migrant Offshore Aid Station), which is based in Malta.
Ackman's donation will cover the purchase of 15 specially equipped Toyota 4x4 Land Cruiser ambulances and the costs of operating them on the front lines.
The Land Cruisers cost roughly $116,000 each and come with an extended roof that let medical personnel stand up as they treat patients.
Ackman, whose great-grandfather emigrated to the United States from Ukraine, has an estimated net worth of $3.5 billion, according to Forbes. Ackman and his wife, Neri Oxman, have pledged to give away the majority of their fortune and have supported causes ranging from medical research to relief to earthquake-stricken Haiti to Harvard University's crew team.