Jafar al-Sadiq in the Tarikh Baghdad:

A man asked him, “Why does the Quran, despite the coming of new and passing of [old generations], only increase in its freshness?” He replied, “Because God did not make it for one specific time or one specific people, so it is new in every age, fresh for every people, until the Day of Judgment.”  (Beirut: Dar al-Kutub al-Ilmiyya, 6:115)

Shared by Professor Jonathan Brown.