Question: We hear that so-and-so was granted authorization by such-and-such a scholar. What does authorization mean? Is it like a testimony that the one authorized is qualified to issue legal verdicts, or does it have another meaning?
Answer—and Allah is the One Who grants success:
Authorization is one of the methods of transmission. It is not permissible for anyone to narrate from a scholar and report from him unless he has heard from him; in that case, it is permissible for him to report from him and narrate what he heard from him. If he did not hear from him, it is not permissible for him to say, “So-and-so said such-and-such,” unless the scholar permitted him to report from him what is contained in such-and-such a book. This permission is called authorization.
Yes, there are well-known books that do not require hearing or authorization, such as Kitāb al-Aḥkām and al-Muntakhab of al-Hādī (Peace be Upon Him). They have reached such a level of fame that they nearly became among the mutawātir works. Thus, whatever books are of this status, it is permissible to narrate them from their author without authorization and without mentioning a chain of transmission.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.3