Shaykh Yasir Qadhi explains and touches base on the topic of Usool Al Hadith in the second part of the three part series.
The process of consolidation of the Sunnah of the Prophet ﷺ was established during the Prophet's ﷺ lifetime. The concept of travelling in the quest for knowledge made a primary base for the preservation of Sunnah. Muwatta Imam Malik wrote the first physical book of hadith almost 120 years after the death of the Prophet ﷺ.
Sahih Bukhari and Sahih Muslim have all the Hadith inside them of pure authenticity. The main 6 works of the Sunan are the following:
Sahih Bukhari
Sahih Muslim
Sunan al-Nasa'i
Sunan Abu Dawud
Sunan al-Tirmidhi
Sunan Ibn Majah
Mishkat al-Masabih , Forty Hadith of An Nawawi, Riyad As Saliheen, Kanz -ul- Ummal are the most common referenced books for Hadith. But they are not the books with Isnad. For the Isnad, one has to go back to the Sahih books.