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You can know that from a number of ways:

1- There isn't any uncorrupted bible anywhere as the Bibles at the time of the revelation of the Quran were all corrupt and altered.

2- There are hundreds of facts that are nowhere to be found in the Bible. Even the stories that are similar are different and more logical and realistic.

3- The fact that the Quran is preserved after more than 1400 years in its original language that hundreds of millions use it till date is a sufficient proof.

4- If all copies of the Quran were to be burnt and destroyed, tomorrow an exact letter by letter copies would be written by the millions of Muslims memorizing it by heart.


Allah says in Quran "There's no changing of Allah's words" how come old scriptures have been changed?