Despite all the exhortations of the Prophet, the Quraish persisted in asking him for a sign. They insisted that unless some sign be sent down to him from his Lord, they would not believe. The disbelievers used to ask: "Why has Muhammad not been sent with miracles like previous prophets?" The Prophet replied: "Because miracles had proved inadequate to convince. Noah was sent with signs, and with what effect? Where was the lost tribe of Thamud? They had refused to receive the preaching of the Prophet Salih, unless he showed them a sign and caused the rock to bring forth a living camel. He did what they asked. In scorn they cut the camel's feet and then, daring the prophet to fulfill his threats of judgment, were found dead in their beds the next morning, stricken by the angel of the Lord."
There are some seventeen places in the Qur'an, in which the Prophet Muhammad is challenged to work a sign, and he answers them all to the same or similar effect: Allah has the power of working miracles, and had not been believed; there were greater miracles in nature than any which could be wrought outside of it; and the Quran itself was a great, everlasting miracle. The Qur'an, the Prophet used to assert to the disbelievers, is a book of blessings which is a warning for the whole world; it is a complete guidance and explains everything necessary; it is a reminder of what is imprinted on human nature and is free from every discrepancy and from error and falsehood. It is a book of true guidance and a light to all.