How can one adopt hadiths that are not narrated in the Two Sahihs, and is adopting them binding, and what are the ranks of hadith books in terms of their binding nature?

For a hadith to be accepted, scholars have stipulated conditions, including the continuity of its chain of narration (isnad), that its narrators are trustworthy and precise, and that it is free from irregularity (shudhudh) or defect (illah). If these conditions of authenticity are met, we rule the hadith to be authentic. It is not necessary for a narrator to have been cited by Bukhari and Muslim in order for him to be deemed trustworthy. Bukhari and Muslim did not commit themselves to transmitting all authentic hadiths. It is well-known that the most authentic books of hadith are those of Bukhari and Muslim, and scholars differed as to which of them is more authentic, with most preferring Bukhari. As for books other than the two Sahihs, they are the rest of the six books: Jami al-Tirmidhi, Sunan Abi Dawud, Sunan al-Nasa'i, and Sunan Ibn Majah. Some scholars include Al-Muwatta instead of Ibn Majah. None of these books is free from hadiths whose chains of narration are not authentic, and these imams did not stipulate the authenticity of all hadiths in their books. As for the general public, they have no alternative but to refer to scholars and ask them about the authenticity or weakness of hadiths.