Of course the chain of transmission accepted by the two schools is not the same.

Of course the chain of transmission accepted by the two schools is not the same. But despite this difference in the authorities who have handed down the prophetic sayings, the actual hadiths recorded by Sunni and Shi'ite sources have overwhelming similarities. The major difference is the Shi'ites' consideration of the extension of an aspect of the being of the Blessed Prophet in the Imams and therefore their addition of the sayings of the Imams to the strictly "prophetic" Hadith .

The sayings of the Imams are in many ways not only a continuation but also a kind of commentary and elucidation of the prophetic Hadith , often with the aim of bringing out the esoteric teachings of Islam. Many of these hadith s deal, like those of the Blessed Prophet, with the practical aspects of life and the Shari'ah . Others deal with pure metaphysics, as do certain prophetic hadith s, especially the "sacred hadith s" ( hadith qudsi ).

Still other sayings of the Imams deal with the devotional aspects of life and contain some of the most famous prayers which have been recited over the ages by both Sunnis and Shi'ites. Finally some of the sayings deal with the various esoteric sciences. They thus cover a vast spectrum ranging from the "mundane" problems of daily life to the question of the meaning of truth itself.

Because of their innate nature and also the fact that like Sufism they issue from the esoteric dimension of Islam, they have intermingled over the ages with certain types of Sufi writings.[^4] They have also been considered as sources of Islamic esotericism by the Sufis, because the Imams of Shi'ism are seen in the Sufi perspective as the spiritual poles of their age.

They appear in the spiritual chain ( silsilah ) of various Sufi orders, even those which have spread almost exclusively among Sunnis.[^5] Because of the nature of their contents, these sayings have influenced nearly every branch of Shi'ite learning as well as the daily life of the community. Shi'ite jurisprudence ( fiqh ) bases itself directly upon this corpus in addition to the Holy Quran. Shi'ite theology ( kalam ) would be incomprehensible without a knowledge of these sayings.

Shi'ite Quranic commentaries draw heavily upon them. Even sciences of nature such as natural history or alchemy were developed with reference to them.