Are the Gospels, the Psalms and the Torah authoritative for Muslims? It doesn’t seem like it. Nevertheless, the Qur’an is supposedly only one part of the larger canon in Islamic thought. Malise Ruthven puts it this way:
At the same time it raises a difficulty about which parts of the scriptures (usually referred to as al-kitab, ‘book’ or ‘writ’, and sometimes umm al-kitab, ‘the mother of scriptures’) are true and which are false. Is the kitab coextensive with the Quran, a kind of divine Ur-text, form which the Quran, like other recognized scriptures (including the Torah of the Jews and the Christian Gospel) derives? A ‘created’ Quran, as a divine artifact, would place the Arabic scripture on the same ontological level as the ‘uncorrupted’ versions of the divine messages delivered to other peoples.