Several classifications of hadiths exist. Specialists in the science of hadith have established several types of classifications. Among the best known: The classification according to reliability (Acceptable = Maqbûl, Authentiques = Sahîh, Bons = Hasan, Inrecevables = Mardûd, Faibles = Dha'îf, Inventés = Mawdû ') and the classification according to the reference of a particular authority. Some authors, like al-Bukharî, have gathered in their collection only the authentic hadiths (Sahîh), the others being simply rejected. The authentic hadiths are reported with the chains of reliable and sure witnesses.