A report by Robert Parry at Consortium News asserts that Saudi Arabia has paid several billion dollars to Israel to lobby in Washington for anti-Iranian positions:
Over the past several years, as both Saudi Arabia and Israel have identified Iran and the so-called “Shiite crescent” as their principal enemies, this once-unthinkable alliance has become possible – and the Saudis, as they are wont to do, may have thrown lots of money into the deal.
According to a source briefed by U.S. intelligence analysts, the Saudis have given Israel at least $16 billion over the past 2 ½ years, funneling the money through a third-country Arab state and into an Israeli “development” account in Europe to help finance infrastructure inside Israel.
The claim is thinly sourced but I regard it as possible. Parry was the first to report the Iran-Contra scandal and has good journalistic credentials. There are many common interests Saudi Arabia and Israel have in Lebanon and Syria as well as in their common position against Iran. Just think about Israel's support for the Saudi financed Jabhat al-Nusra in the Golan heights.
But the common interests between Saudi Arabia and Israel, documented in Parry's piece, are also entirely plausible without any money paid by Saudi Arabia.
A slush fund of that size, if it exists at all, can hardly be hidden for long. If there is some truth to the claim I expect more confirming leaks.
Until then let us file this under "rumor".