Scholars who spent a great deal of their lives with the hadith of the Prophet (peace be upon him) developed a sense which they could use instantly in detecting error. Their example was like that of a man who lived with a beloved friend for scores of years, knew him very well in every situation and so could easily say which statement belonged to him and which not. Similarly, a literary critic who studies a poet for a long time and becomes fully acquainted with his style can, on the basis of his perception and personal experience, easily detect a poem which does not belong to the poet. However, Muhaddithin (hadith scholars) did not depend solely on personal experience as it may be counted a form subjective criticism. In short, if a hadith was not transmitted by any trustworthy scholar, and there was a liar or a person accused of lying in the chain of transmission it was said to have been fabricated by that person.
However, scholars laid down certain rules according to which one could reach conclusions about the spuriousness or genuineness of hadith even without going into detailed study of isnad (chain of narration). Here is a summary of the method described by Ibn al-Qayyim.
Ibn al-Qayyim's description of general rules about rejections of hadith are as follows:
- If the hadith contains an exaggerated statement that the Prophet could not have made. For example, a false hadith attributed to the Prophet that when one pronounces 'La ilaha ill Allah' God creates from this sentence a bird with seventy thousand tongues.
- Experiment rejects it.
- Ridiculous kind of attribution.
- Contradicts a well known Sunna.
- Attributes a statement to the Prophet which was supposed to have been made in the presence of a thousand Companions but all of them supposedly concealed it.
- The statement has no resemblance to other statements of the Prophet.
- Sounds like the saying of mystics or medical practitioners.
- Contradicts the clear and obvious meanings of the Quran.
- Inadequate in its style.
Besides these rules, the entire system of isnad was applied to detect fabrication.
"Studies in Early Hadith Literatures" - Mustafa al-Azami, pp. 71, 72