Claim that the Sunnah cannot be trusted
Question

                Some people reject the Sunnah on the basis that there are many weak and fabricated ahaadeeth and that the fabrications of many liars weaken the Sunnah and make it such that it cannot be trusted. What is your opinion about this claim?
Praise be to Allah.This 
          is the view of some heretics and misguided people, both in the past 
          and nowadays. In modern times, those who expressed this view include 
          Saalih Abu Bakr in his book al-Adwaa’ 
          al-Qur’aaniyyah; Husayn Ahmad Ameen in Daleel al-Muslim al-Hazeen; Ahmad Ameen in Fajr 
          al-Islam; ‘Abd-Allaah al-Na’eem in Nahwa Tatweer al-Tashree’  
          al-Islaami; Sa’eed al-‘Ashmaawi in Haqqeeqat 
          al-Hijaab; Saalih al-Wardaani in his misleading book Rihlati 
          min al-Sunnah ila al-Shee’ah; ‘Abd al-Jawaad Yaaseen in al-Sultah fi’l-Islam; Nasr Abu Zayd in Imaam 
          al-Shaafa'i; Zakariya ‘Abbaas Dawood in Ta’ammulaat 
          fi’l-Hadeeth; Hawlat Nahr in Diraasaat 
          Muhammadiyyah; Maurice Bucaille in  Diraasat 
          al-Kutub al-Muqaddisah; Murtada al-‘Askar in Khamsoon 
          wa Mi’ah Sahaabi Mukhtalaq; Dr. Mustafa Mahmood in Maqaalaat 
          ‘an al-Shafaa’ah.
We 
          say: it is true that there were fabricators and liars who made up words 
          and attributed them to the Messenger of Allaah  
          (peace and blessings of Allaah be upon him), but the matter is not quite 
          so simple as imagined by those doubters who also spread doubts among 
          others. They are unaware of the facts about how the Muslims took care 
          of the Sunnah. Alongside the fabricators, there were great numbers of 
          narrators who were trustworthy and highly skilled, and a large number 
          of scholars who surrounded the hadeeths of the Messenger of Allaah  
          (peace and blessings of Allaah be upon him) with a strong barrier which 
          was difficult for the liars to penetrate. By means of their vast knowledge 
          and deep insight, these muhaddithoon (scholars of hadeeth) were able 
          to spot the liars and understand their intentions and motives, and they 
          were able to detect everything that was falsely attributed to the Messenger 
          of Allaah  (peace and blessings 
          of Allaah be upon him). These fabricators were not given free rein to 
          do as they wished with the ahaadeeth of the Prophet  
          (peace and blessings of Allaah be upon him), and they were given no 
          room to penetrate the ranks of trustworthy narrators of ahaadeeth without 
          being detected.
Who 
          else exposed the lies of these kaafirs, heretics and extreme innovators?
Who 
          were the ones who gave us the definition of what is fabricated, the 
          reasons for fabrication, different types of fabrications and the signs 
          by which a fabricated report may be recognized?  Who wrote so many 
          books on this issue?
They 
          are the guardians of Islam, the vicegerents and troops of Allaah on 
          His earth. They are the brilliant scholars of whom Haaroon al-Rasheed 
          spoke when he arrested a heretic and ordered that he be executed. The 
          heretic said, “Why are you executing me?” Haaroon al-Rasheed said, “To 
          rid the people of you.” The heretic said: “O Ameer 
          al-Mu’mineen, what will you do about the thousand ahaadeeth 
          – according to one report, four thousand ahaadeeth – which I have fabricated 
          and spread among you, in which I made what is halaal haraam and what 
          is haraam halaal, of which the Prophet uttered not one letter?” Haaroon 
          al-Rasheed said to him: “What will you do, O enemy of Allaah, about 
          Abu Ishaaq al-Fazaari and ‘Abd-Allaah ibn al-Mubaarak? They will go 
          through them and sift them letter by letter.” (Tadhkirat 
          al-Huffaaz by al-Dhahabi, 1/273; Taareekh 
          al-Khulafaa’ by al-Suyooti, p. 174).
Professor 
          Muhammad Asad said: “The existence of fabricated ahaadeeth cannot be 
          taken to prove that the entire system of hadeeth is not to be trusted, 
          because these fabricated ahaadeeth never deceived the muhadditheen as 
          some European critics claimed, oversimplifying the matter, and as was 
          echoed by some who claim to be Muslims.” (al-Islam ‘ala Muftaraq al-Tareeq, p. 96) 
We will end this 
          discussion by quoting what was said by Imaam Ibn al-Qayyim al-Jawziyyah: 
          Imaam Abu’l-Muzaffar al-Sam’aani said: “If they say: there are too many 
          reports in the hands of the people and they have become confused, we 
          say: no one is confused except those who are ignorant. Those who have 
          knowledge of them (the reports) check them as stringently as those who 
          deal with money check dirhams and dinars. So they single out (and discard) 
          the false reports and keep the good reports. If there happens to be 
          a narrator who made a mistake, this will not go unnoticed by the brilliant 
          scholars of hadeeth. These scholars listed the mistakes made in both 
          the isnaad (chain of narrators) and matn (texts) of  reports; so 
          you can see that for each narrator they made a list of the mistakes 
          that he had made and the letters that he had mispronounced. If the mistakes 
          of the narrators – in both the isnaad and the matn – did not go unchecked, 
          then how could the fabricated ahaadeeth manufactured by the heretics 
          have slipped past those brilliant scholars?  How could people have 
          narrated ahaadeeth from heretics without the scholars noticing? That 
          is the view of some heretics, but no one would say such a thing except 
          one who is ignorant, misguided, an innovator and a liar who wants to 
          undermine the saheeh ahaadeeth and true reports of the Prophet  
          (peace and blessings of Allaah be upon him) and confuse ignorant people 
          by means of this lie. There is no evidence for rejecting the reports 
          of the Messenger of Allaah  (peace 
          and blessings of Allaah be upon him) that is weaker or more impossible 
          than this. The one who voices this view deserves to be silenced and 
          expelled from the Muslim lands.