Surah 37. As-Saffat, Ayah 168

Lit., "a reminder (dhikr) from those of old": see note [27] on verses {69-70} above. Most of the commentators assume that the term dhikr connotes here, as so often in the Qur'an, a "divine writ". In my opinion, however, it is far more probable - because more in tune with the context - that in this case it signifies an ancestral tradition bearing on the (to them astonishing) message of God's oneness and uniqueness as promulgated by the Qur'an.

 The “Reminder” mentioned here refers to Scriptures such as the Torah and the Gospel. It is commonly used in the Quran as another name for Islam’s holy book.