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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.