The science of hadith has not been without critics. According to Muhammad Husayn Haykal, "despite the great care and precision of the Hadith scholars, much of what they regarded as true was later proved to be spurious." He goes on to quote Al-Nawawi (1233–1277), who stated that "a number of scholars discovered many hadiths" in the two most authentic hadith collection Sahih al-Bukhari and Sahih Muslim "which do not fulfill the conditions of verification assumed by these men" (i.e. by the hadith collectors Muhammad al-Bukhari and Muslim ibn al-Hajjaj).