This is taken from 'al-Baa'ithul Hatheeth Sharh Ikhtisaar 'Uloomul Hadeeth' - Shaykh Ahmad Shaakir's commentary on 'Ikhtisaar 'Uloomul Hadeeth' by al-Haafidh Ibn Katheer, (p. 13-16)
So here I would like to point out the benefit of this knowledge humbly called, 'mustalahahul hadeeth' (the science of hadeeth), and its effect upon the divinely-revealed, and historical sciences, and other than them from the various types of sciences which are established from the authentic texts, and which rely upon it.
So verily the Muslims - from the first generation - had a great concern for memorization of the chains of narration in their Revelation from the Book and the Sunnah, the like of which no nation from before them had. So they memorized the Qur`aan, and they reported from the Messenger of Allaah (sallallaahu 'alayhi wa sallam) frequently, sentence by sentence, and word by word, and letter by letter. They preserved it in their chests, and they confirmed it upon pages of their writings, and they authored books about it with exhaustive detail. They also memorized much about their Prophet (sallallaahu 'alayhi wa sallam), everyone of his statements or actions or conditions. He was a teacher from his Lord, and an explainer of His Revelation, and a commander of the establishment of His Religion. All of his (sallallaahu 'alayhi wa sallam) statements and actions and conditions are an explanation of the Qur`aan. He is the infallible Messenger and the good example. Allaah the Exalted says in describing him:
"He does not speak from desire. Verily it is not but Revelation revealed to him." [Sooratun Najm 53:3-4]
"And We revealed to you the Reminder for you to explain to the people what has been revealed to them, in the hopes that they may become thoughtful." [Sooratun Nahl 16:44]
Allaah also says:
"Indeed there is a good example for you in the Messenger of Allaah." [Sooratul Ahzaab 33:21]
'Abdullaah Ibn 'Umar Ibnul 'Aas used to write everything he heard from the Messenger of Allaah, so the Quraysh forbade him from that and it was mentioned to the Prophet (sallallaahu 'alayhi wa sallam). So he said: "Write. So by the One in Whose Hand my soul is, nothing emanates from me except truth."  The Prophet (sallallaahu 'alayhi wa sallam) commanded the Muslims in the farewell pilgrimage to teach about him as a general command. So he said: "So let the one who is present teach the one who is absent. So it may be that the one who is being taught may be more heedful than him."  He also said: "So let the one who is present teach the one who is absent, for the one who taught may be more heedful than the one who heard directly."  So the Muslims understood that all this was obligatory upon them. They memorized everything about the Prophet (sallallaahu 'alayhi wa sallam) and they acted upon that, and they went to great lengths to fulfill this trust, and they related hadeeths from him; either as well known (mashhoor), or with authentically established chains of narrations. According to the scholars, this is named an authentic hadeeth (hadeeth saheeh) or a good hadeeth (hadeeth hasan).
The scholars of hadeeth took great care to make sure they collected everything that was narrated from him as a narration, even if it was not authentic. Then they strove to authenticate every hadeeth, and every letter narrated in a narration. So they criticized their conditions and their narrations and they took the most extreme care in quoting. So they would rule a hadeeth to be weak due to a little doubt in the biography of a narrator's character which affected his reliability according to the people of knowledge. So if they doubted in his truthfulness and they knew that he had lied about something in his statements, then they would discard his narrations and they would call his hadeeth fabricated (mawdhoo') or lies (makdhoob), even if he was not particularly known for lying in narrating hadeeths and even though they knew the liar could have been telling the truth.
Likewise, they used to check the memorization of every narrator and read his narrations with other ones. So if they found many mistakes from him and his memorization was not good, they would declare his narrations weak, even if he had not been disparaged in his character or his truthfulness. It was feared that his memory might be unreliable in his narrations.
Indeed they wrote and compiled the fundamental principles that were required for the acceptance of hadeeth, so these are the fundamental principles of this field of study. So they refined them with as close examination as humanly possible, so as to preserve their Religion. So the fundamental that they established became the soundest fundamentals for confirming historical accounts and the finest and the most delicate, even though it is despised - in these later times - by most of the people since they do not have adequate knowledge about it or clarification.
So the scholars of many different sciences followed them in this. So the scholars of language and the scholars of literature and the scholars of history and other than these imitated them. So they made efforts to relate everything of their sciences with a chain of narrators, as you will see in the older books. So the foundations of this knowledge were used with the intention of authenticating narrations in anything that involved narrating. So this knowledge is the basis for any narration-based science.
Along with this however, there were some people who innovated a vile innovation. They alleged that hadeeths could not be used as proofs because, in some conventions, it was called 'uncertain affirmation' (dhanniyyatuth thuboot). This means that it was not affirmed with concurrency (tawaatur) requiring absoluteness in narrations. So they concluded that such narrations do not provide conclusive knowledge. This group did not realize that the term 'definitive knowledge' was just a convention among some scholars to be applied to some sciences only. In the case of hadeeth however, the most authentic reports were declared authentic by any scholar who had studied hadeeth, even if it was not concurrent (mutawaatir). If they were to reject every non-recurrent narration, then they should first eliminate every science that relies upon narration; including history. However, at that time, the group that went with such a bad opinion was small, overwhelmed, and they did not have any influence upon Islaamic sciences.
However in this century, there has appeared a new group who alleged the same old allegations and more. They claim that all hadeeths are unauthentic and baseless, so it is not allowed to use them as proofs in matters of the Religion. Some even went to the point of rejecting all the rules and fundamental set for hadeeth checking; and started authenticating hadeeths according to desires and feelings, without any particular rule or proof. For these people, there is no cure except if they learn Islaamic knowledge and have respect for it, and Allaah guides whomever He wills.
So as for the attack upon authentic hadeeths, and the doubt in their attribution to the Prophet (sallallaahu 'alayhi wa sallam), then this is nothing less than an announcement of war against the Muslims for those who do it despite knowledge. It is also due to ignorance and lack of study for those who blindly follow the first group. So the meaning of this doubt and attack is that all the reliable narrators from amongst the Salafus-Saalih were untrustworthy liars. It necessitates accusing them of either telling lies and misleading the people, or of ignorance and stupidity. Indeed Allaah rescued them from these things, and they knew the reality of the statement of the Messenger of Allaah: "Whoever lies upon me deliberately, then let him take his seat in the Fire."  He also said: "Whoever relates a hadeeth from me and thinks that it is a lie, then he is one of the liars." 
So the one who accuses them of lying has passed a judgement which is free of any good quality and which will cause him to dwell in the Fire. This is because lying is from the greatest of major sins, then it is from the most evil of qualities and the worst of them. No nation shall succeed if lying is common among its people, even if it is in small matters. So what about telling lies in the Religion and about the best of the Messengers (sallallaahu 'alayhi wa sallam)? Indeed the people of the first generation of Muslims - and in the first three generations - were the best of the people and the highest in character and they were the most fearful of Allaah. So due to that, Allaah aided them and gave them victory and opened many counties to them and they came to rule many nations in a few years. This was because of their Religion and beautiful character before it was due to their sword and spear.
 This is taken from 'al-Baa'ithul Hatheeth Sharh Ikhtisaar 'Uloomul Hadeeth' - shaykh Ahmad Shaakir's commentary on 'Ikhtisaar 'Uloomul Hadeeth' by al-Haafidh Ibn Katheer, (p. 13-16)
 Related by Ahmad in his Musnad (no. 6510)(2/162) with an authentic chain of narrators. It is also related by Abu Daawood and al-Haakim and other than them in meaning.
 Related in Fathul Baaree (1/46) and others.
 See Fathul Baaree (3/459).
 Shaykh al-Albaanee has declared it to be an authentic concurrent hadeeth, he records 63 different routes for it. See: Mukhtasar Saheeh Muslim (no. 1861-1862), Rawdhun Nadheer (no. 707), and Saheehul Jaami' (no. 6519).
 Related by Abu Dardaa', reported by Ahmad, Muslim, and Ibn Maajah. Shaykh al-Albaanee has declared it authentic in Saheehul Jaami' (no. 6199), and from Samoorah and Mugheerah (no. 1863), also see ad-Da'eefah (1/12).