The unique style of the Qur’an (the holy book of Islam) which was revealed 14 centuries ago, and the superior wisdom it represents are definite proof that it is the word of Allah.
Additionally, the Qur’an has many miraculous aspects which prove that it is sent by Allah. One of them is that some scientific facts, which we have only been able to discover by the technology of the 20th century, were stated in the Qur’an 1400 years ago.
These facts which could not have been known at the time of the Qur’an’s revelation once again show to the man of today that the Qur’an is the word of Allah.