Imām Abū Naṣr ʿUbaydillāh al-Sijzī (d. AH 444) said:

“Know, may Allāh, the Glorified have mercy upon us and you, that this section is from the most important sections of this book without question because of the calamities and confusion that has appeared [as a result of the failure to implement this] and because of what has been introduced to the people due to their negligence of this matter.

This is because the affairs of the people of this time have changed and those who can be truly depended upon are scarce. How many people sell their religion for a lowly price or to endear themselves to those who are perceived to be large in number? Lies are commonly attributed to the various schools of thought (madhāhib). So it becomes obligatory upon every Muslim who wishes to escape from this to not rely upon everyone and to not depend upon every book. He should not surrender his reins to everyone who outwardly claims to be in agreement with him… Whoever desires safety and security from the likes of these people and to be free of any innovations must make the Book (the Qurʾān) and the narrations his scale which he uses to measure everything that he sees and hears. If he is knowledgeable concerning these things, he will constantly refer back to them and do so while following the example of the salaf.

He should not accept any statement from anyone except that he asks them to provide validation for their claim in the form of a clear verse (of the Qurʾān), an established Sunnah or a statement of a companion from a chain of narrators that is authentic. In addition, he should beware of the works of those whose conditions have changed for indeed in those works there are scorpions and perhaps for their venom there is no antidote.”