Depending on the number of narrators, hadiths are classified into two general categories: mutawatir (consecutive) and ahad (single). Mashhur (famous) hadiths are also classified into the ahad group.

A mutawatir hadith is one that is reported by a large number of narrators about whom it is inconceivable that they would agree to tell a lie. This condition must be met throughout the chain, from the beginning to the end. Moreover, the hadith should be based on the senses, such as on something that was heard or seen. With these characteristics, a mutawatir hadith conveys certain knowledge and cannot be criticized. 

A mutawatir hadith is called lafzan (verbally) mutawatir, if it is reported verbatim in each narration. It is widely accepted that this kind of hadith is quite rare.

The common meaning is called ma'nan (in meaning) mutawatir, if the hadith is reported by narrators who meet the tawatur requirements of different judgments with points in common. There are many hadiths of this kind.

An ahad hadith is one which fails to fulfill the requirement of mutawatir. Therefore, most hadiths are ahad hadiths, as they do not fulfill the requirements of tawatur. In this sense, almost all hadiths in our hadith books are of this kind.

There are also some hadiths that were ahad hadiths at the beginning but achieved tawatur status in following generations (the tabi'un - successors - or Atba' al-Tabi'in - persons belonging to the second generation after the Prophet). These hadiths are called mashhur hadiths. These hadiths must be reported by at least two narrators from each generation.