Surah 2:4:
"And who believe in that which is revealed unto thee and that which was revealed BEFORE thee, and are certain of the Hereafter".
This verse establishes the continuity of revelation as a requirement for the believer. The Quran demands faith in the prior scriptures without qualification.
This verse does NOT say:
"believe in the original versions that are now lost."
It uses the past tense verb unzila ("was revealed") to describe a body of work that the audience is expected to recognize.
If the Torah and Gospel were already corrupted by the 7th century CE, the Quran is commanding Muslims to believe in "corrupted" books to be considered righteous.
There is NO "qualification clause" in this verse stating that the previous revelations are no longer authoritative or have been altered beyond recognition.
The absence of a warning here suggests that the scriptures in the hands of Jews and Christians during the 7th century CE were considered valid by the Quran.
If the Quran is the "Criterion" (Al-Furqan), it must have something stable to judge against.
If the "revelation before you" is untrustworthy, then the Quran’s claim to confirm it (as seen in 2:97 or 5:48) becomes a confirmation of a lie.
Surah 2:97:
Say, 'Whoever is an enemy to Gabriel - it is he who has brought the Qur'an down upon your heart, by permission of Allah, CONFIRMING that which was before it and as guidance and good tidings for the believers'".Surah 5:48:
"And We have revealed to you, the Book in truth, CONFIRMING that which preceded it of the Scripture and as a criterion over it. So judge between them by what Allah has revealed and do not follow their inclinations away from what has come to you of the truth. To each of you We prescribed a law and a method. Had Allah willed, He would have made you one nation, but to test you in what He has given you; so race to good. To Allah is your return all together, and He will inform you concerning that over which you used to differ".