The legendary daggers Tiriosh, Nightmare of the Ages and Golad, Twilight of the Aspects, better known as "Fangs of the Father" appeared during patch 4.3 of the Cataclysm expansion. These are obtained through a quest line exclusively dedicated to thieves.
Here I suggest you discover the 13 quests that allow them to be obtained, divided into 3 parts.
Part I: Terror and Veangeance
1 / prove your worth
This is the first quest that can be obtained from Lord Afrasastrasz directly in the Dragon Soul raid. She asks you to retrieve a Cryptomancer Decoder Ring from the corpse of Hagara the Stormbinder.
2 / A hidden message
Lord Afrasastrasz wants you to use the Cryptomancer's Decoder Ring to decrypt a scroll Corastrasza will give you when found in the Twilight Highlands.
3/ Direction Ravenholdt
This quest requires you to speak to Mostrasz.
4 / to capture a thief
This quest is an infiltration mission in Ravenholdt Manor to find the stolen Black Dragon Egg. Here is a video that shows how to proceed to complete this scenario:
You will need to return the quest to Deathwing's son, who we will also meet during Mists of Pandaria for the legendary cloak: Irion.
5 / Our man is in Gilneas
You will need to find Zazzo Golden Fingers in the Ruins of Gilneas.
6 / Assassinez I believe
You will have to use your ability to infiltrate again in order to find and kill Hiram Credo. Just like the first infiltration, here's a video that might help you out.
7 / The act is recorded
Here is the quest marking the end of a first stage since at the end of it you will receive two epic daggers. But before that, Irion asks you to make your quest. After which, Terror and Vengeance will be yours.
Part II: Sleeper and Dreamer
1 / Pick up the rosaries
The long part of your epic begins in the Soul of the Dragons as Irion asks you to collect 333 Dark Gems which can be obtained from the Elementium Gem Strings, themselves obtained from all the bosses of the Soul of the Dragons raid. , no matter how difficult. However, I recommend the heroic 25 mode since the rosaries will be more numerous!
2 / Our man is in Karazhan
You will have to make your report after bringing back the gems. To do so, go find Zazzo Doigts-d'Or south of Karazhan, he is waiting for you there.
3 / The blood of the traitor
Here is your 3rd infiltration quest which will lead you to the ruins of Karazhan. Your mission is to kill Nalice and bring back the Vial of Black Dragon's Blood.
4 / victory in the depths
Go back to Irion, you will have to give him your Terror and Vengeance daggers as well as the Vial of preserved dragon's blood which is provided to you by the quest. Your reward will be significant: Sleeper and Dreamer.
Part III: The Father's Fangs
1 / sharpen your fangs
As the quest announces, you are in the home stretch. This quest also asks you to return to find 60 Strings of Elementium Gems, still in the Soul of the Dragons. But this time, you will not be able to open the rosaries.
This is the last quest of your adventure. Irion asks you to go kill Deathwing, who is none other than his father, to retrieve a Fragment of Deathwing Jawbone. Once the artifact is in your possession, return to Irion so that he grants you your salvation: Tiriosh, the Nightmare of the Ages and Golad, the Twilight of the Aspects.
I wish you good luck !