In the time of Imam As-Suyuty (911 AH) a Muslim sect attacked the Sunnah and refused to hold it as a proof. Thereupon, Imam As-Suyuty exerted a lot of efforts to defend the Sunnah and wrote a book to refute their claims which was entitled: Muftah Al Jannah fi Al Ihtijaj bissunnah (The key of Paradise to hold the Sunnah as a proof). He wrote in the introduction: "Let it be known that there is a kind of knowledge that is like medicine and there is a kind of opinions that is like bathrooms that are not mentioned or meant except at necessary. However, something occurred recently, but had rooted long time ago which is: Rafidi heretic people has spoken lengthy and badly about the Prophetic Sunnah and the reported Hadiths (may Allah exalt and raise their honor) and claimed that they should not be held as a proof. They claimed that only the Qur'an should be held as a proof, then mentioned the following Hadith: (what has been reported from me, compare it to the Qur'an, if you find a source (matching the same meaning), then take it (and act accordingly), otherwise reject it). Thus, I as well as other people heard this speech from him. Some people did not pay attention to it while others neither know the origin of this speech nor from where it emerged. So, I decided to explain to the people the origin of this speech, explain its falsehood, and to show its bad consequences on Muslims." (1)
As-Suyuty spoke about the origin of that corrupt speech saying: The origin of that corrupt opinion is that heretics and a group of the Rafidah (a Shi`ah group denying the caliphates of Abu Bakr As-Siddiq and `Umar ibn Al Khattab, making accusations against them and many other Companions of the Prophet) refused to hold the Sunnah as a proof and depended only on the Qur'an as a proof. They were of different doctrines: Some of them believed that prophethood was basically came to Ali and that Gabriel (Peace be upon him) had made a mistake by descending on the Master of Prophets (i.e., Muhammad peace be upon him) may Allah be Exalted of what they claim. Some of them admitted that the Prophet (peace be upon him) was the original prophet but said: Caliphate was genuinely the sole right of Ali, but when the Companions gave homage to Abu Bakr (may Allah be pleased with him), those wretched people (may Allah curse them) said: The Companions have converted from Islam when they oppressed Ali and gave homage to someone who did not deserve it. Moreover, they claimed that Ali (may Allah be pleased with him) was a disbeliever because he did ask for his right. As a result, they rejected all Hadiths because they were reported by disbelievers, indeed we are possessed by Allah and indeed to Him we shall return.
It was not permissible to mention those opinions, but it was necessary to mention them to explain the corrupt opinion of those people." (2)
As-Suyuty (may Allah be merciful with him) mentioned that the people who used to hold these opinions were present abundantly in the time of the Four Imams (Abu Hanifah, Malik, Al-Shafi`y, and Ahmad) and those who followed them. The great Four Imams (Abu Hanifah, Malik, Al-Shafi`y, and Ahmad) and their companions refuted their claims in their lessons and debates. (3)
Furthermore, As-Suyuty mentioned in his book many sayings of great scholars before him, confirming that holding the Sunnah as a proof is a fundamental basis of religion, as he reported their refutations to the claims of that corrupt doctrine.
(1) Muftah Al Jannah p. 11.
(2) Muftah Al Jannah p. 12.
(3) Ibid. p. 12.