This is the case with the evidence to which Allah Most High draws attention in His Noble Book: the parables He sets forth and other evidence pointing to His oneness, the truthfulness of His messengers, the affirmation of His attributes, and the resurrection. All of these are rational proofs whose validity is known through reason. They are rational demonstrations and inferences, yet they are also Sharia-based.
Alternatively, Sharia-based evidence may be known solely through the report of a truthful informant. When he reports something that can be known only through his report, that evidence is both Sharia-based and received through hearing.
Many speculative theologians think that Sharia-based evidence is confined to the report of a truthful informant, and that the Quran and Sunnah provide evidence only in this way. They therefore divide the fundamentals of religion into two categories: matters known through reason and matters known through hearing. They regard the first category as something that cannot be known through the Quran and Sunnah.
This is an error on their part. Rather, the Quran points to rational evidence, explains it, and draws attention to it, although some rational evidence is known through direct observation and its implications. As Allah Most High says:
“We will show them Our signs on the horizons and within themselves until it becomes clear to them that it is the truth. Is it not enough that your Lord is a Witness over all things?” [Fussilat: 53]
If, however, “Sharia-based” means what the Sharia permits and authorizes, this includes what the truthful informant reports, what the Quran indicates and draws attention to, and what existing things indicate and attest to.
The Lawgiver forbids the use of an argument because it is itself false—for example, when one of its premises is false. Such an argument is a lie, and Allah forbids lying, especially lying about Him. As Allah Most High says:
“Was not the covenant of the Scripture taken from them, that they would say nothing about Allah except the truth? And they had studied what was in it.” [Al-Aʿrāf: 169]