These three categories can be subdivided into a number of specific reasons.

The first reason:

The hadith may not have reached him. Someone whom a hadith has not reached is not required to know the ruling it entails. If it has not reached him and he has ruled on the matter according to the apparent meaning of a Quranic verse or another hadith, or on the basis of analogy or the presumption of continuity, his ruling may sometimes agree with that hadith and sometimes differ from it.

This is the predominant reason why statements of the early generations are found to conflict with certain hadiths, for no one in this community has had comprehensive knowledge of all the hadiths of the Messenger of Allah—may Allah bless him and grant him peace. The Prophet—may Allah bless him and grant him peace—would speak, give a legal opinion, pass judgment, or do something, and those present would hear or see him. They, or some of them, would convey it to others, so that knowledge of it would reach whichever scholars Allah willed among the Companions, the Successors, and those who came after them.

Then, on another occasion, he might speak, give a legal opinion, pass judgment, or do something, witnessed by some who had been absent from the earlier gathering. They would convey it to whomever they could. Thus, one group would possess knowledge that the other did not, and the other would possess knowledge that the first did not. Scholars among the Companions and those who came after them differ in merit according to the breadth or depth of their knowledge. As for any one person having comprehensive knowledge of all the hadiths of the Messenger of Allah—may Allah bless him and grant him peace—