﴿ وَإِنَّهُۥ لَفِى زُبُرِ ٱلْأَوَّلِينَ ﴾

“And, verily, [the essence of] this [revelation] is indeed found in the ancient books of divine wisdom [as well].”

(And lo, it is) i.e. the description of the Qur'an and Muhammad (pbuh) (in the Scriptures of the men of old) is written in the Scriptures of the prophets who came before you.