"There was a point during the Yom Kippur War of October 1973 when it appeared that the Egyptians had broken though Israeli lines in the Sinai at the same time the Syrians were about to drive across the Golan. Although never verified, it’s been reported on some authority that Moshe Dayan placed the Israeli nuclear strike force on full alert, the planes at the ends of the runways with their engines hot, their weapons armed, ready to head for their targets."
This partially correlates with the analysis of Walter J. Boyne in the book, The Yom Kippur War, and the Airlift that saved Israel, pub. 2002. As he explains it, though, there was no Egyptian side to the threat, which also correlates with other things I've read. Though the Egyptians broke through very strong in the Sinai, they then halted and dug in.
The Syrians on the other hand, did seem poised to break through with their tanks in the Golan. The generally accepted story is that extremely heroic actions by a small group of Israeli tanks stopped the Syrian advance at a crucial point.
Boyne, however, a retired U. S. Air Force colonel, has carefully analyzed the battle and come up with the conclusion that this storyline is, in fact, impossible. He simply believes the number of Israeli tanks in the area was way too small to stop the strong Syrian advance that was in progress. He has come to the conclusion that the Syrian advance was stopped by an explicit, albeit discrete, threat from the Israeli government to obliterate Damascus with nuclear weapons. All his evidence for this however is indirect, as I have stated above. He simply cannot conceive of any other explanation for what happened.
I can say that the book appears to be well researched, well-written, and intelligently expressed. However, I don't have any other information.
I can see Israel delivering such a back-channel maessage.