U.S. investor Warren Buffett, speaking at a campaign rally for Democratic presidential candidate Hillary Clinton, challenged Republican Donald Trump on Monday to release his tax return and let people ask the two of them questions about their finances.

Clinton threw her weight behind the idea during the campaign stop in Omaha, Nebraska.

“I want to throw in to the challenge that Warren made. If this congressional district has the highest percentage of votes in any congressional district, and of course, if I win, here’s what we’ll do. Shortly after I become, sometime as soon as I can arrange it, come back here, and Warren and I will dance in the streets together,” Clinton said.

Trump has said he would not release his returns until the Internal Revenue Service has completed an audit.