Sonny Bill Williams loaned Anthony Mundine half a million dollars before his bout with Danny Green

Rugby star Sonny Bill Williams lent his friend Anthony Mundine A$500,000 before his recent bout with Danny Green.

There was no contract or paperwork, just a handshake, Australia's Sunday Telegraph revealed.

The All Blacks star sent half a million dollars to Mundine for a family emergency under an Islamic finance arrangement where there are no interest payments, according to the Sunday Telegraph.

The newspaper reported that Mundine owns five homes but is believed to have made some poor investments and has given away a lot of his money.

Like Williams, Mundine is a former rugby league star-turned boxer who converted to Islam after being managed by boxing promoter Khoder Nasser.

"He could have sold one of the properties to get the money but Sonny wanted to help out," Nasser told the Sunday Telegraph.

Reports said Mundine and Green made about A$4 million each out of the super fight. "I'll pay him back as soon as I get paid next week," Mundine said.

Sonny Bill Williams and manager Khoder Nasser at the ASB Classic tennis in 2012. Photo / Norrie Montgomery

They practise Islamic finance, a Sharia law-compliant form of lending which forbids interest charges on loans.

"It's very hard to explain our brotherhood in words," Mundine told News Corp.

"I didn't understand it until I became a Muslim.

"We'd literally die for each other. We trust and love each other."

In 2008, Mundine lent Williams A$750,000 when he abruptly left the Canterbury Bulldogs league side to play rugby union with French rugby club Toulon.

Williams had recently signed with Nasser.

Earlier this month, Green defeated Mundine in Adelaide to retain his Australian cruiser-weight title.

The report said Mundine had expenses ahead of that fight, including flights and accommodation for his team in South Australia.

Anthony Mundine lost on points to Danny Green at Adelaide Oval on February 3. Photo / Getty Images

WHAT IS ISLAMIC FINANCE?

Islamic finance is a form of Sharia law-compliant lending.

It's a $2 trillion global industry, which bans interest payments on debt.

It could include an Islamic mortgage, where a bank buys a property first before lending the money.

The borrower then buys the property back from the bank at a high price and repays the money in installments.

The products have existed since the mid-1970s, but the principles have existed since the seventh century.

Source: The Economist

- This story originally appeared in the Daily Mail