This quest is not available in game.
Speak with Garrosh Hellscream at Grommash Hold in Orgrimmar's Valley of Wisdom.
You have successfully defended Orgrimmar from the threat posed by this Twilight's Hammer cult, <name>, and without shedding the blood of our own people. Our enemy will not rest for long. I cannot imagine that Cho'Gall will accept defeat so easily.
Garrosh Hellscream is a well-known hero of the Horde and he will know how to deal with this matter. Go to the Valley of Wisdom and speak to him in Grommash Hold. Tell young Hellscream that our enemies have shown themselves and we must be prepared for their return.