Al Nusrah Front (al Qaeda affiliate in Syria) release a video showing fighters from the Caucasus in Hama, Syria give bayah (pledge allegiance) to Ayman al Zawahiri, the head of al Qaeda.
This pledge also requires members to fight IS if attacked by them.
According to pro opposition twitter accounts, there has been a certain amount of discourse between groups within coalitions regarding what to do about IS. Some groups want to attack IS, others do not, some will fight IS if attacked, others wont.
Jund al Aqsa (Soldiers of al Aqsa) a fundamentalist Islamic group used to be part of the al Nusrah Front until it became independent for a number of reasons. One of the reasons being the al Nusrah Front opposition to IS.
It was until yesterday the 24 October 2015, part of Jaish al Fatah (the Army of Conquest), a coalition made up of influential fundamentalist Islamic groups in Syria which generally oppose IS as well as the Syrian government. It includes groups such as the al Nusrah Front and Ahrar ash Sham.
It seems the IS issue has never been adequately resolved between these groups and Jund al Aqsa has decided to part ways with the coalition, one of the many reasons due to pressure exerted from Ahrar al Sham to fight IS if they decide to attack positions in the future.
- Statement by Jund al Aqsa regarding split from Jaish al Fatah (24 Oct 2015):