The reason for this is that, if reason could establish no obligations or prohibitions, a person reflecting on the matter could not infer that Allah, glorified be He, does not speak falsely or support a liar with a miracle. For, according to them, before revelation there is no rational basis for judging this to be evil or contrary to wisdom.
If that were so, a rational person could not rule out the possibility that any report received from Him was false, or that any miracle he witnessed had been used to support a lying fabricator. This would prevent acceptance of revelation from heaven and submission to the evidence of prophetic miracles that attest to the truth of prophethood.
Since this view must be rejected, and one must believe that Allah—exalted is His majesty—is far above lying or supporting a fabricator with a miracle, it follows that these things are evil and forbidden according to reason, and precluded by wisdom.”
I say: This is a well-known argument among those who hold that reason can judge good and evil.
They say that through it they know that Allah is far above doing anything evil, such as lying or confirming the truthfulness of someone falsely claiming prophethood by granting him a miracle that attests to his truthfulness. Although this is possible and within His power, He does not do it because it is evil and contrary to wisdom.
They say that this is how the truthfulness of the prophets is known.
Those who dispute their position—such as al-Ash‘arī and his followers, Ibn Hāmid, al-Qādī Abū Ya‘lā, Ibn ‘Aqīl, Ibn al-Zāghūnī, and others—follow a different route to establishing the truthfulness of the prophets.
Either they follow the argument from divine power—as al-Ash‘arī did in one of his two positions, as did the two judges, Abū Bakr and Abū Ya‘lā, and others—namely, that there is no way to attest to a prophet’s truthfulness other than a miracle. Thus, if a miracle did not signify such attestation, it would follow that the Creator was incapable of attesting to the truthfulness of His messengers.