The Jews Alter Allah's Words
Allah states that some Jews, may Allah's curses descend on them, distort Allah's Words with their tongues, change them from their appropriate places, and alter their intended meanings. They do this to deceive the ignorant people by making it appear that their words are in the Book of Allah. They attribute their own lies to Allah, even though they know that they have lied and invented falsehood. Therefore, Allah said,
وَيَقُولُونَ عَلَى اللَّهِ الْكَذِبَ وَهُمْ يَعْلَمُونَ
(and they speak a lie against Allah while they know it.)
Mujahid, Ash-Sha`bi, Al-Hasan, Qatadah and Ar-Rabi` bin Anas said that,
يَلْوُونَ أَلْسِنَتَهُم بِالْكِتَـبِ
(who distort the Book with their tongues,) means, "They alter them (Allah's Words)."
Al-Bukhari reported that Ibn `Abbas said that the Ayah means they alter and add although none among Allah's creation can remove the Words of Allah from His Books, they alter and distort their apparent meanings. Wahb bin Munabbih said, "The Tawrah and the Injil remain as Allah revealed them, and no letter in them was removed. However, the people misguide others by addition and false interpretation, relying on books that they wrote themselves. Then,
وَيَقُولُونَ هُوَ مِنْ عِندِ اللَّهِ وَمَا هُوَ مِنْ عِندِ اللَّهِ
(they say: "This is from Allah," but it is not from Allah;)
As for Allah's Books, they are still preserved and cannot be changed." Ibn Abi Hatim recorded this statement. However, if Wahb meant the books that are currently in the hands of the People of the Book, then we should state that there is no doubt that they altered, distorted, added to and deleted from them. For instance, the Arabic versions of these books contain tremendous error, many additions and deletions and enormous misinterpretation. Those who rendered these translations have incorrect comprehension in most, rather, all of these translations. If Wahb meant the Books of Allah that He has with Him, then indeed, these Books are preserved and were never changed.
Tafsir Ibn Kathir (abridged, English).