This is what I found on Thottbot.

link

Corrupted Ashbringer
Binds when picked up
Two-Hand Sword
259 - 389 Damage Speed 3.60
(90.0 damage per second)
Durability 120 / 120
Requires Level 60
-25 Stamina
Equip: Inflicts the Will of the Ashbringer upon the wielder
Equip: Improves your chance to get a critical strike by 2%
Equip: Improves your chance to hit by 1%
Chance on Hit: Steals 185-216 life from target

It makes you friendly with the Scarlet Crusade and hostile to the Argent Dawn. It allows you to talk to Mograine the son in order to start the quest to achieve the REAL Ashbringer but it leads you to Outland so you could only get it in the Burning Crusade.

Thanks

So these four horsemen drop corrupted and then yu have to talk to morgraine son