and others like him call rational truths, whereas they are nothing but ignorant notions.

His ignorance of both leads him to regard certain unsound questions and means as fundamentals of religion when they are not, and to suppose that the Messenger did not explain what ought to be believed concerning these matters. This is indeed the case among various groups of people—even their most proficient members, let alone ordinary people. For the fundamentals of religion consist either of matters that must be believed and affirmed in word, or in both word and deed—such as questions concerning Allah’s oneness, His attributes, divine decree, prophethood, and the life to come—or of the evidence for these matters.

As for the first category:

Everything that people need to know, believe, and accept as true concerning these matters has been explained by Allah and His Messenger in a thorough manner that leaves no excuse. These are among the most important matters that the Messenger conveyed clearly and explained to people, and among the most important matters concerning which Allah established proof against His servants through the messengers who explained and conveyed them. Allah’s Book, whose wording and meanings the Companions and then their Successors transmitted from the Messenger, together with the wisdom—that is, the Sunnah of Allah’s Messenger—which they likewise transmitted from him, encompasses these matters to the fullest extent intended, including all that is obligatory and recommended.

All praise is due to Allah, who sent us a Messenger from among ourselves, reciting His verses to us, purifying us, and teaching us the Book and wisdom; who perfected our religion for us, completed His favour upon us, and approved Islam as our religion; who sent down the Book as a detailed explanation of all things, and as guidance, mercy, and glad tidings