Billionaire Elon Musk taunted the United Nations with an offer to sell some of his Tesla stock if the agency can prove $6 billion would solve world hunger. His tweet came in response to UN World Food Programme (WFP) Director David Beasley’s comments calling on the world’s two wealthiest men—Musk and Amazon founder Jeff Bezos—to “step up now, on a one-time basis” and donate the money. “If WFP can describe on this Twitter thread exactly how $6 billion will solve world hunger, I will sell Tesla stock right now and do it,” tweeted Musk. “But it must be open source accounting, so the public sees precisely how the money is spent.”

Beasley responded to Musk on Twitter, assuring him the WFP was fully transparent and the public can “be totally confident of such.” He doubled down on his earlier comment, saying, “$6 billion will not solve world hunger, but it WILL prevent geopolitical instability, mass migration, and save 42 million people on the brink of starvation.”