29.48 – You were not accustomed to read from any book before it, or to write it with your right (hand)
The Quran continues to address the messenger directly (vv. 45–54), here apparently claiming that his recitations could only come from Allah. If the messenger could neither read nor write, according to this claim, then he could have neither copied from another book nor written out of his own thoughts (see also comments at 7.157).