"Ahl al-Kalam" agreed with "Ahl al-Hadith" that the example of Muhammad, the prophet of Islam, was authoritative, but it did not believe it to be divine revelation, a status that only the Quran had (in its view). It also rejected the authority of hadith on the grounds that its corpus was "fill with contradictory, blasphemous, and absurd" reports, and that in jurisprudence, even the smallest doubt about a source was too much. Thus, they believed, the true legacy of the prophet was to be found elsewhere. "Ahl al-Hadith" prevailed over the "Ahl al-Kalam" (and Muslims, or at least mainstream Muslims, now accept the authority of hadith) so that most of what is known about their arguments comes from the writings of their opponents, such as Imam al-Shafi'i. Brown also describes the Muʿtazili as "the later "ahl al-kalām"", suggesting the "ahl al-kalām" were forerunners of the Muʿtazili. Even though seeking knowledge in Islam is considered a religious obligation, the study of kalam is considered by Muslim scholars to fall beyond the category of necessity and is usually the preserve of qualified scholars, eliciting limited interest from the masses or common people. The early Muslim scholar al-Shafi‘i held that there should be a certain number of men trained in kalam to defend and purify the faith, but that it would be a great evil if their arguments should become known to the mass of the people. Similarly, the Islamic scholar al-Ghazali held the view that the science of kalam is not a personal duty on Muslims but a collective duty. Like al-Shafi‘i, he discouraged the masses from studying it. The Hanbali Sufi, Khwaja Abdullah Ansari wrote a treatise entitled "Dhamm al-Kalam" where he criticized the use of kalam. The contemporary Islamic scholar Nuh Ha Mim Keller holds the view that the criticism of kalam from scholars was specific to the Muʿtazila, going on to claim that other historical Muslim scholars such as al-Ghazali and an-Nawawi saw both good and bad in kalam and cautioned from the speculative excess of unorthodox groups such as the Muʿtazila and the Jahmis. As Nuh Ha Mim Keller states in his article "Kalam and Islam":