The great legal scholar and founder of one of the four schools of Islamic Law, Imam Mālik, said: “I did not issue a single legal verdict until seventy authorities attested that I was qualified to do so.”
He also said: “I consulted with Rabī`ah and Yahyā b. Sa`īd, and both of them ordered me to do so.”
Someone asked him what he would have done if the two of them had told him otherwise. Mālik replied: “Then I would have refrained from doing so. A man should not regard himself as qualified for something until he consults with those who are more knowledgeable than he is.”
This was the practice of the Pious Predecessors. Al-Shāfi`ī did not start giving his own lessons until after his teacher Muslim b. Khālid al-Zanjī authorised him to do so. Al-Shāfi`ī was either fifteen or eighteen when this happened. This is when his teacher said to him: “By Allah, the time has come for you to issue legal verdicts.”
This practice persisted throughout history, with the teacher authorising the student by issuing a document affirming that the student has mastered a particular book or subject and is now permitted to teach it to others.
This permission was known in Arabic as the ijāzah
, and was the equivalent of what we call a diploma today. Indeed, in many countries in the Muslim worlds, schools and universities call their diplomas bythis name.
Historically, three qualities were considered before a student would be issued this diploma.
 The first was age. Student would have to be at an age where their mental faculties were fully mature. This was not firmly fixed. Some scholars regarded seventeen as a suitable minimum age. Others set it at twenty. There were even those who saw fifty as a suitable minimum age for being authorised to issue legal verdicts.
 The second quality was knowledge. Regardless of the student’s age, it was mandatory for the student to have a mastery of the Qur’an, Sunnah, and the tools of legal reasoning. The student would also have to be conversant with the points of scholarly consensus and disagreement. This was essential to avoid the possibility of issuing verdicts that contradicted the sacred texts or the unanimous agreement of the Muslims.
 The third quality was balanced judgment, meaning that the student should not be mentally weak, deficient in understanding, or lazy in thinking. The student should have sound ideas and be free from extreme or deviant tendencies.
Mālik’s nephew Ismā`īl b. Abī `Uways says that his uncle told him while standing outside the Prophet’s mosque in Madinah:
This knowledge is our religion, so take care from whom you take your religion. I met seventy men under the pillars of this mosque who related things from the words of Allah’s Messenger, but I did not take anything from them. If one of them was given the trust of the public treasury, he would have fulfilled that trust perfectly. The reason I did not take from them is that they were not properly qualified in this field, whereas Ibn Shihāb came to us in his youth and we used to crowd around his door.
Mālik considered the proficiency that comes with specialization to be indispensable.
Al-Qarāfī described those who speak about Islamic legal matters as people “acting as interpreters of Allah’s intent”.
Ibn al-Qayyim described them as “signatories in Allah’s name”.
This is a grave responsibility. Reputation is not enough, nor age, nor extensive reading. Those who wish to embark upon this endeavour must possess a large number of qualities. By issuing legal verdicts, the scholars are assuming the responsibility of the Prophets. Indeed, they are the inheritors of the Prophets.