Surah 52:1-3:
By the Mount. And a Book inscribed. In parchment unrolled.
The surah opens by swearing an oath by At-Tur (the Mount, universally understood in Islamic tradition as Mount Sinai, where God spoke to Moses) and a "Book inscribed in parchment unrolled" (Kitabin masturin fee raqqin manshoor).
This is a direct acknowledgement of the physical, written transmission of the Mosaic revelation. A book written on raqq (parchment/vellum) that is manshoor (unrolled/opened) describes the exact format of the Hebrew Torah scrolls kept and read by the Jewish community.
The Quran is swearing an oath by the validity of this unrolled parchment. If the text written on the scrolls held by the Jews was corrupted and untrustworthy, why is Allah using it as a sacred, cosmic oath to prove his own truthfulness? An oath is only as reliable as the object being sworn by. Swearing by a corrupted, falsified book would invalidate the very warning Allah is trying to issue in this surah.