Travel into Tempest Keep and slay Al'ar while wearing the Ashtongue Cowl. Return to Akama in Shadowmoon Valley once you've completed this task.
Olum's sacrifice was tremendous. I would never have asked him to give up his life myself. But it is done.
If we're to lure Illidan back into a false sense of security, we need to do his bidding - at least for now.
I command a vast army of Ashtongue, but - aside from the Deathsworn - none can be trusted.
You are to perform the deed that Illidan demands. Take this cowl; it is magical in nature. You will appear to be one of my men to any who see you slaying Kael's phoenix, Al'ar.