From the book, "The Textbook of Hadith Studies" by Mohammad Hashim Kamali: Chapter 7: "Hadith Forgery":
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Extensive forgery in hadith was commonly known and acknowledged to have occurred in the early decades of the advent of Islam. It is believed to have begun following the turmoil over the murder of the third caliph, Uthman, which dealt a heavy blow to the unity of the umma. This momentous event is held responsible for the emergence of serious political differences and partisan groups such as Shia, Kharijites and Mutazila, as well as the onset of forgery in hadith. Hadith forgery was to a large extent an epiphenomenon of these developments and the conflicts they precipitated eventually led to the collapse of the early caliphate barely forty year after its inception.
A forged hadith or al-mawdu, may be defined as a report, invented by a liar, who has attributed it to the Prophet and it may include either the text or both the text and isnad of the report. Even if this is done with a pious purpose in order to promote what is deemed to be a good cause, it would still count as a forgery and no credibility would be given to the motive and purpose of a deliberate forgery. Hadith forgery has not been confined to isolated cases but took rather a wide dimension barely before the end of the first generation of Muslims in Madina. A part of this phenomenon has been associated with the expansion of the territorial domains of the Islamic state and the ever increasing number of new immigrants of Persians, Romans, Egyptians, Syrians and others who were easy prey to misguided influences against hadith.
The historical origins of forgery in hadith are somewhat uncertain. While some observers have given the caliphate of Uthman as a starting point, others have dated it a little later, at around the year 40 hijra, when political differences between the fourth caliph, Ali and the governor of al-Sham, Muawiya, led to military confrontation and the division of Muslims into various factions. According to a third view, forgery in hadith started even earlier, that is, during the caliphate of Abu Bakr when he waged the war of apostasy (ridda) against the refusers of zakah. But the year 40 is considered the more likely starting point for the development of serious and persistent differences in the community. Muslims were thus divided and hostility between them acquired a religious dimension when they began to use the Qur'an and Sunna in support of their claims. When the misguided elements among them failed to find any authority in the sources for their views, they either imposed a distorted interpretation on the source material, or embarked on outright fabrication.
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Forgery in hadith is believed to have begun in the context of personality cults (fada'il -al-ashkhas) which aimed to credit or discredit leading political figures with exaggerated claims. An example of this is the following statement attributed to the Prophet: "Whoever wished to behold Adam for his knowledge, Noah for his piety, Abraham for his gentleness, Moses for his commanding patience and Jesus for his devotion to worship - let him behold Ali."
Political differences between Ali and Abu Bakr, Ali and Muawiya, Ali and Aisha, between Abd Allah b. Zubayr and Abd al-Malik b. Marwan, and generally between the Umayyads and Abbasids were among the causes for hadith forgery. Numerous fabricated hadith have thus been recorded in condemnation of Muawiya including, for example, the one in which the Prophet is quoted to have ordered the Muslims "When you see Muawuya on my pulpit, kill him." The fanatical supporters of Muawiya and the Umayyad dynasty are, on the other hand, known to have fabricated hadith such as "The trusted ones are three: I, Gabriel and Muawiya." Political motives also seem to be behind the so-called hadith, for example, that "When the caliphate reaches bani al-Abbas, it will not leave them until they surrender it to Jesus the Son of Mary."
The heretic faction known as al-Zanadiqa, (pl. of Zindiq), owing to their hatred of Islam, fabricated hadith which discredited Islam in the view of its followers. Included among such are: "eggplants are a cure for every illness"; and "beholding a good-looking face is a form of ibada". It is reported that just before his execution at the time of Caliph al-Mahdi, one of the notorious fabricators of hadith, Abd al-Karim b. Abu al-Awja, confessed that he had fabricated 4,000 ahadith in which halal was rendered haram and haram was rendered halal. It has been further reported that the Zanadiqa have fabricated a total of 14,000 ahadith, a report which may or may not be credible. For a statement of this nature tends to arouse suspicion as to its veracity: even in fabricated matters, it is not a facile task to invent such a vast number of hadith on the subject of halal and haram.
Known among the classes of forgers are also professional story-tellers and preachers (al-qussas wa al-waizun) whose urge for popularity through arousing emotional response in audience led them to indulge in forgery. They made up stories and attributed them to the Prophet.
Juristic and theological differences constitute another theme of forgery in hadith. The ulama were thus divided into the Ahl al-Sunna, Mutazila, Jabriyya, Murijia etc., and they disagreed over many issues, such as the attributes of God, the definition of faith (iman), whether faith is only a state of mind or that it relates to both belief and conduct, whether faith is liable to increase or decrease, whether the Qur'an is created or uncreated and so forth. Some of these differences are known to have led to exaggerated statements, even forgery, in hadith.
Another category of fabricated hadith is associated with the religious zeal of individuals whose devotion to Islam led them to careless ascription of hadith to the Prophet. This is illustrated by the forgeries committed by Nuh b. Abi Maryam on the virtues of the various suras of the Qur'an. He is said to have later regretted what he did and explained that he fabricated such hadith because he saw people who were turning away from the Qur'an and occupying themselves with the fiqh of Abu Hanifa and the battle stories of Muhammad b. Ishaq and that he did so as part of carrying out hisba, that is promoting good and forbidding evil, and that he "lied for the Prophet and not against him". This is considered as one of the worst forms of forgery as it almost succeeds to be convincing and becomes difficult to isolate.
Other themes of hadith forgery include the urge on the part of courtiers who distorted hadith so as to please and flatter their overlords. Similarly, the desire to establish the permissibility or virtue of certain varieties of food, beverages, clothes and customary practices has led to forgery in the hadith. A number of fabricated hadiths have thus been recorded on the virtues of food items such as rice, lentils, aubergines, and places such as Asqalan, months of the year, days and even certain times of the day, and also of personal names such as Ahmed and Muhammad.
Qur'an commentaries (tafsir) in both the tafsir bil-mathur (commentary based on precedent) and tafsir bil-ray varieties have not escaped forgeries especially in regard to what is known as Jewish anecdotes (Israliyat). It is noted in this connection that prior to Islam when the Bedouin and illiterate strata of the Arabian people wanted to learn more about certain subjects such as the origins of creation and its mysteries, turmoil and fitna, and so forth they asked the Jews and Christians who has known of such subjects from the Torah and the Bible. Later when these people converted to Islam they conveyed the information they had in their commentaries and elaborations on the Qur'anic passages, especially on subjects outside the area of the ahkam. Some of the recognised names among the ahl al-kitab such as Abd Allah b. Sallam, Kab al-Ahbar, and Wahb b. Munabbih were famed for their anecdotes and stories some of which then found their way into the context of the Qur'anic commentaries. Since these were stories and anecdotes outside of the ahkam, their veracity was often overlooked. "The Qur'an commentaries treated these relatively lightly and filled their tafsir works with such anecdotes ... " that were of questionable origin and content. (Ibid p. 345.)
NOTE: To see the full article on Hadith in Islam, click here.