or you ascend up into heaven, and even then we will put no faith in your ascension till you bring down for us a letter that we can read." Say [٠, Mui:Jammad]: "Glorified is my Lord! Am I naught save mortal messenger?" (Q. ١٧:٩٠-٩٣)

The conclusion which the opponents [of our view] have drawn from these verses is that the unbelievers asked the Prophet to work a miracle which would testify to the truthfulness of his prophethood; but he refused, and admitted his inability, claiming for himself only that he was a mortal sent to them as a messenger. Hence, the verses indicate that the working of miracles was denied him.
The response is as follows:
First, we have already explained to the reader, in our response to the preceding arguments, the circumstances of the demanded signs. The miracles that the unbe‌ lievers asked the Prophet to perform were undoubtedly demanded signs, and the unbelievers were predisposed to be obstinate in denying the truth. This is indicated by two things:
١. They had made their acceptance of the Prophets call conditional upon one of those things that they were demanding. Had they not been obstinate in denying the truth, they would have been satisfied with any divine sign that proved his truthfulness. There was no other reason for them to demand these things specifically to the exclu‌ sion of other divine signs.
٢. Regarding their saying, "Or you ascend up into heaven, and even then we will put no faith in your ascension till you bring down for us a letter that we can read," what is the point of the stipulation to bring down a letter? Is not ascending to heaven a sufficient sign in itself of his veracity? Or is there not in these vain desires clear evidence of their obstinacy against the truth?

Second, some of the things demanded by the unbelievers in the verses above were impossible [demands] and others were no proof of the truthfulness of a claim to prophethood. Even if it were incumbent on the Prophet (peace be upon him) to ac‌ quiesce in their demands, these would not have been the kinds of miracles for him to perform.
To make this clear, there were six things that the Mekkan unbelievers demanded from the Prophet in these verses; three of them were impossible, and three, though not impossible, had no connection with establishing the truthfulness of a claim to prophethood.
The first of the three inconceivable things was causing heaven to fall upon them piecemeal. This would entail the destruction of the Earth and the death of its inhabi‌ tants. Such a thing would occur only at the end of time. The Prophet had informed them about this, as is evident from their saying, "As you have asserted." The falling of heaven on the Earth is mentioned in several places in the Quran, as in Gods saying:

When the heaven is split asunder (Q.. ٨٤:١); when the heaven is cleft asunder (Q. ٨٢: I). If We will, We can make the earth swallow them or cause obliteration from the sky to fall on them (Q. ٣٤:٩).

What makes this inconceivable is that its occurrence before its appointed time is incompatible with the survival of mankind and the guidance toward their perfection that wisdom has determined. It is impossible for the All-Wise to act in a way that is incompatible with His wisdom.