chapotraphouse

I guess there's the Sunni-Shia divide that's of interest here. Iran (shia) is Israels arch-enemy. Al-Qaeda (as well as it's offshoots like ISIS) is led by Sunni jihadists. They too are generally considered enemies by Israel, but in the grand scheme of things they are (currently) a much smaller threat than Iran and it's allies. Al-Qaeda and Iran themselves are each others enemies, and since 'the enemy of your enemy is your friend', Israel sometimes benefits from the presence of Al-Qaeda. They formed a sort of buffer for them. This report tells us Israel was treating Al-Qaeda fighters wounded in the Syrian civil war. So it's very clear that Israels and Al-Qaeda interests sometimes align. Were Al-Qaeda ever to become more powerful than Iran is, then Israel would obviously shift their focus, since a powerful Al-Qaeda would also be a clear threat to them. Any pan-islamist organization would deem the presence of Israel on the Levant a blemish. Israel is often seen as a sort of colonial state that treats their Muslim population as second class citizens at best. The biggest threat to Israel would be Muslims uniting under any one pan-islamist flag, so Israel has a vested interest in division so they play the divide and rule game. All this is not to say though, that Al-Qaeda is a Mossad front. Their actions can be explained by their interests sometimes aligning, so according to Occam's razor we shouldn't rely on the assumption of them being a Mossad front. We don't need that assumption to explain what we are seeing. AFAIK there hasn't been any proof of the theory. This PolitiFact article looks into the Hornet’s Nest-theory, wherein US and Israel created ISIS to sow division in the Middle East, and PolitiFacts deems it an unfounded conspiracy theory.

Discalimer: not an expert in any sense, just my best take.