Brother, it may be very difficult for you to understand as I know you are Shia. According to the Shiite scholars, The Science of Hadith in the Madhab of The Twelvers has never existed nor was it implemented before the 900s Hijri.
The Big Scholar Al Ha’iri “الحائري” In His book Muktabas el Athar “مقتبس الأثر” part 3 page 73 says: “From the Information that No One doubts is that No one worked in The Science of Hadith from our scholars before the second Shaheed”
And the second Shaheed is Al Hassan Bin ZaynulDeen al Jab’ee al Amili “الحسن بن زين الدين الجبعي العاملي ” (Died 965 hijri).
On the other hand, well organised science of Hadeeth, with strict conditions to avoid inclusion of fabricated hadeeths was established 200 years after the death of Prophet (pbuh).
Sahih Bukhari, collected by Imam Bukhari (d. 256 AH, 870 CE), includes 7,275 ahadith (2,230 without repetitions)
Sahih Muslim, collected by Muslim b. al-Hajjaj (d. 261 AH, 875 CE), includes 9,200 ahadith (2,200 without repetitions)
Sunan Abu Dawood, collected by Abu Dawood (d. 275 AH, 888 CE), includes 4,800 ahadith
Jami al-Tirmidhi, collected by al-Tirmidhi (d. 279 AH, 892 CE), includes 3,956 ahadith
Sunan al-Sughra, collected by al-Nasa'i (d. 303 AH, 915 CE), includes 5,270 ahadith
Sunan ibn Majah, collected by Ibn Majah (d. 273 AH, 887 CE), over 4,000 ahadith
The two most highly respected collections of hadith are the authenticated collections the Sahih Bukhari and Sahih Muslim. (Sahih literally means "correct, true, valid, or sound."). there is Ijma-e_Immat on the authenticity of these two books.
In addition to these, four other collections came to be well-respected, although not to the degree of Bukhari and Muslim's sahih collections. These four other collections are the Sunan of Tirmidhi, Nasa'i, Ibn Majah, and Abu Da'ud. These four books have 60 - 80 % authentic Hadeeths. Work has already been done by Muhadiseen to identify the weak and fabricated hadeeths included in all of the above books.