وَما كُنتَ تَتلو مِن قَبلِهِ مِن كِتابٍ وَلا تَخُطُّهُ بِيَمينِكَ ۖ إِذًا لَارتابَ المُبطِلونَ

You didn’t recite any scripture before this or write one with your right hand. If you had, the fabricators of falsehood would have doubted.