They derived all that from the light of the Imams of guidance...
They derived all that from the light of the Imams of guidance, the progeny of Muhammad, peace be upon him and them, quoting it from their own oceans of knowledge, hearing it directly from them. They are the scribes of their knowledge and wisdom. Their works were authored during the life-time of those purified ones, and such works became references for all Shi’ahs who succeeded them. Through them, the superiority of the sect of manifested itself over all other Islamic sects.
We do not know any follower of the four Sunni Imams, for example, who authored a book during the life-time of their Imams. Rather, people authored works in abundance dealing with their faith after those Imams had left this world, when it was decided that taqlid should be confined to their sects alone.
During their life-time, they were just like any other contemporary jurist or traditionist, not enjoying any distinction over others of their class; therefore, nobody among their contemporaries was interested in exerting an effort to record their speeches like that exerted by Shi’ahs in recording the statements of the Infallible Imams (as). Ever since the inception of the Shi’ah sect, nobody was permitted to refer in the religious matters to anyone other than their Imams.
For this reason, such an effort was unavoidable, and they became the sole source of religious scholarship. A great deal of effort and resources were spent in recording their verbal statements, and many exhausted their resources in doing so in a manner that is unmatched so that they might preserve the knowledge which, according to such sect, is the only one accepted by Allah.
The books authored during the life-time of Imam al-Sadiq (as) alone numbered four hundred dealing with four hundred different topics containing the religious verdicts [ fatawa ] issued by al-Sadiq (as) during his life-time. The disciples of al-Sadiq (as) have written many, many times this number, as you will hear in detail shortly, Insha-Allah. As regarding the four Sunni imams, nobody looks at them in the eyes Shi’ahs look at the Imams of .
Nay; they did not even have followers during their own life-time! They did not live to enjoy the status given to them after they had died, as stated by Ibn Khaldün al-’Arabi in a chapter he dedicated to the science of fiqh in his famous Introduction, and it is a fact admitted by many of their renown scholars.