The Quran

133

وَقالوا لَولا يَأتينا بِآيَةٍ مِن رَبِّهِ ۚ أَوَلَم تَأتِهِم بَيِّنَةُ ما فِي الصُّحُفِ الأولىٰ

Muhammad Asad

NOW THEY [who are blind to the truth] are wont to say, "If [Muhammad] would but produce for us a miracle from his Sustainer!¹ [But] has there not come unto them a clear evidence [of the truth of this divine writ] in what is [to be found] in the earlier scriptures?²

I.e., in proof of his prophetic mission: cf. 6:109 and, many other instances in which the deniers of the truth are spoken of as making their belief in the Qur'anic message dependent on tangible "miracles".
I.e., "Does not the Qur'an express the same fundamental truths as were expressed in the revelations granted to the earlier prophets?" Beyond this, the above rhetorical question contains an allusion to the predictions of the advent of Muhammad to be found in the earlier scriptures, e.g.. in Deuteronomy xviii, 15 and 18 (discussed in my note 33 on 2:42) or in John xiv, 16, xv, 26 and xvi, 7, where Jesus speaks of the "Comforter" who is to come after him. (Regarding this latter prediction, see my note on 61:6.)