The Shaykh replied (al-Fataawa 1/236):
Knowledge is what Allaah said and what His Messenger said and it is not what so and so says. Knowledge is what Allaah said and what His Messenger said, after that is the speech of the people of knowledge (Ahlul-‘Ilm) with which they explain it [knowledge] and clarify it to the people. The people of knowledge (Ahlul-‘Ilm), after the Messengers, are the Vicegerents (Khulafaa) of Allaah amongst His servants.
The Mighty and Most High mentions:
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Allaah bears witness that Lâ ilâha illa Huwa (none has the right to be worshipped but He), and the angels, and those having knowledge (also give this witness); (He is always) maintaining His creation in Justice. Lâ ilâh illa Huwa (none has the right to be worshipped but He), the All-Mighty, the All-Wise. (Aali-Imran 3:18).
And true knowledge is to have knowledge of Allaah and His religion.
He the Most High said:
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It is only those who have knowledge among His slaves that fear Allaah. (Faatir (35): 28)
And they are the Messengers and their followers the people of foresightedness, the people of religion, the people of truth and the people of the Qur’aan and the Sunnah. So the scholars are the successors of the Messengers and they clarify and direct to Allaah and His religion.
The student of knowledge does not become from the people of knowledge except by learning and contemplating upon the Book of Allaah and the Sunnah of His Messenger (Õáì Çááå Úáíå æÓáã) and taking from the scholars of the Sunnah. This is the path of knowledge; that is occupying oneself with being upon obedience, contemplation, comprehension, gaining benefit and that he reads the books which are beneficial for the student of knowledge from the beginning to its end. He should contemplate, comprehend and carefully read that which is difficult for him in the reliable books of at-Tafseer (exegesis of the Qur’aan), like the Tafseer of Ibn Katheer and al-Baghawee and their likes from reliable books of Tafseer. He concerns himself with the distinguished books of Hadeeth and takes knowledge from the scholars of Ahlus-Sunnah wal-Jamaa’ah from the people of insight; and not from the scholars of al-kalaam (rhetorical speech and philosophy) and not from the scholars of innovation or the ignoramuses.
So the knowledge that is not from the book of Allaah and Sunnah of His Messenger is not called ‘ilm (knowledge) rather it is called Jahl (ignorance). Even though it maybe beneficial knowledge concerning the Dunya (worldly matters); but the intent is [knowledge] which benefits in the Hereafter, rescues from al-Jahaalah (Ignorance of the religion), gives insight to a person in the religion and acquaints him to what Allaah has obligated upon him and prohibited him from. This is al-‘Ilm ash-Shar’ee (legislated knowledge).