The Qur`anic statement that the Bible has been tampered with is proven by historical facts as we learn from Biblical scholars themselves.

As for the Jewish scriptures, they were burnt down at least three times in their entirety; each time they were put together from memory.

Internal examination of scriptures also reveals so many contradictions in the Old Testament:  To cite one example:

Moses is considered the author of the first five books of the Bible; the Pentateuch (Deuteronomy 31:24). Scholars ask:

How could Moses be the author of Deuteronomy when his obituary is also listed as the last chapter:

Deuteronomy 34:1–12

Then Moses went up from the plains of Moab to Mount Nebo, to the top of Pisgah, which is across from Jericho. And the Lord showed him all the land of Gilead as far as Dan . . . . So Moses the servant of the Lord died there in the land of Moab, according to the word of the Lord. And He buried him in a valley in the land of Moab, opposite Beth Peor; but no one knows his grave to this day. Moses was one hundred and twenty years old when he died. His eyes were not dim nor his natural vigor diminished…

As for the Christian scriptures, it is also a fact that they come from many different authors who wrote biographies of Jesus in different periods of history, and every author gave the title of Gospel: thus, gospel according to Mathew, Mark, Luke and John; these four were selected out of a greater number of such gospels; they were widely different from each other. It does not take a lot of imaginations to know that gospel revealed to Jesus cannot be but one; so, where is it in its original form.

I also wish to cite here an interesting observation made the late Professor Muhammad Hameedullah about the attempts of the Christian clergy of Germany to collate the ancient manuscripts of the Bible; since the original in Aramaic (the language of Jesus) is extinct, the oldest available Bible is in Greek, from which it has been translated into all the other language. Thus, they collected all the available manuscripts in the world and the report published after this global exercise stated, “Some two hundred thousand contradictory narrations have been found” and “of these one-eight are of an important nature.

As for the views of the modern academic scholars in regard to the forgeries, contradictions, and tampering  with the scriptures, you may refer to the works of  Professor Bart Ehrman; here are three of them:

Misquoting Jesus: The Story Behind Who Changed the Bible and Why by Bart Ehrman

Jesus Interrupted: Revealing the Hidden Contradictions in the Bible (And Why We Don`t Know About Them) by Bart Ehrman

Forged: Writing in the Name of God–Why the Bible`s Authors Are Not Who We Think They Are by Bart Ehrman

Professor Ehrman was a conservative evangelical Christian, who was driven by his religious zeal to study the history of the Bible; however, in the process of his life-long search after the truth, he has lost his faith!

Almighty Allah knows best.