In Reading Is Fundamental, Prophet Kevin Tran translates the Leviathan tablet which reveals the existence of a weapon capable of killing Leviathan. One of the pieces is noted to be "the bone of a righteous mortal."
In There Will Be Blood, the Winchesters discuss finding the remaining pieces of the weapon with Dean pointing out that they don't have any leads on a "righteous bone." When the Winchesters summon Crowley for his blood, he tells them that he will only give them his blood last, after they have acquired all of the other ingredients which includes the bone.
In Survival of the Fittest after getting the blood of the Alpha Vampire, the Winchesters travel to the crypt of a convent in search of a dead nun they believe to be righteous enough to fit the criteria. The two eventually settle on Sister Mary Constant and rob her grave. Castiel later examines the bone they took from her grave and admits it to be a good choice. Once the Winchesters have all of the bloods they need, they pour it over the bone, turning it into the weapon. With the aid of Castiel, Dean is later able to use the weapon to kill Dick Roman and end the Leviathan threat on Earth.
- Dean calls this a "righteous bone" in There Will Be Blood when discussing finding the pieces of the weapon to kill the Leviathan.
- In Survival of the Fittest, Dean uses a second bone on Dick Roman to trick him into lowering his guard so he could kill him. While its unclear where the bone came from, its possible its a second bone taken from the grave of Sister Mary Constant, meaning it may have counted as a second righteous bone.