Except for Iran's allies Syria, Hezbollah, & Hamas, I would expect the local muslim reactions to be a mix of glee & fear.
Glee because 2 Sunni enemies, Shia Iran & Israel are destroying each other. Fear of a widening of the war to engulf them & fallout that might be a nightmare.
I would expect no Sunni muslim nation to side with Iran. They could not assist in a nuclear war, & only add themselves to an Israeli target list. Pakistan would not expend its nuclear arsenal with arch enemy India next door. Saudi Arabia is forever neutered for fear Mecca & Medina will become huge glass parking lots with a gigantic hole in the middle. Turkey would be limited by NATO.
As for Iran's allies mentioned above, this is an especially crazy lot. I expect many of these fools to rush into Israel to “reclaim Palestine”, only to die of radiation poisoning. A particularly fitting end for them, I think, & another Middle East problem solved. Beyond that fantasy, a mortally wounded Israel might opt to nuke all its enemies, & I wouldn't blame them.
I've considered this and think that there is a real possibility that it might happen. If (Heaven forbid) Iran succeeds in nuking Israel and kills upwards of one million people, Israel will be sorely wounded, but not killed. They might therefore fear that some of the other muslim nations, primarily Syria, Egypt, Libya, and Saudi Arabia (who all have chemical weapons and some have biological weapon stockpiles) would take the opportunity to finish them off while they are crippled.