First off:
Reforging The Sword - Quest - World of Warcraft
1. Set the instance to normal, run into the Pit of Saron and grab the 2 Saronite right inside. Run out, reset, repeat.
You can't solo the the boss but the next part is the more important thing to solo, as it saves you from running a whole instance.
For the quest:
http://db.************.com/q/24476/tempering-the-blade/
You can stealth the entire duration of the instance. However, there are a couple of things to note. Most noticeably that there is 1 group of mobs who all are facing outwards, make sure to distract or they will almost guaranteed to aggro you.
There is also a mob known as Spectral Warden, this mob is immune to distract, when it comes down the hall make sure you run around it while it is in the middle of one of the "sections" and it will turn to face you but should not aggro.
Lastly, the Crucible of Souls does not spawn until you engage the Devourer of Souls. However, you can get around this by stealthing behind him and the crucible (the pedestal thing behind the boss) and popping evasion from stealth then immediately popping cloak of shadows and then hitting the boss with 1 move, THEN vanish, the crucible will have spawned and the boss will have disappeared so use your quest item and temper your blade then exit the instance.
In numerical form:
1. Stealth behind boss.
2. Pop Evasion
3. Pop Cloak of Shadows
4. Attack Boss once
5. Vanish
6. Use quest item
7. Leave
Druids can do this too, except they have to die. Once you die you can release and come back and run back to the boss and the crucible will still be up. However, you just need to use the quest item from your inventory from stealth and then die again, and you'll be all set!
Hope this helps, I'll have a video coming shortly but I have to get it converted.