وَإِنْ كُنْتُمْ فِي رَيْبٍ مِمَّا نَزَّلْنَا عَلَى عَبْدِنَا فَأْتُوا بِسُورَةٍ مِنْ مِثْلِهِ وَادْعُوا شُهَدَاءَكُمْ مِنْ دُونِ اللَّهِ إِنْ كُنْتُمْ صَادِقِينَ.
If you are in doubt about what We have sent down upon Our servant, then produce a sūrah like it and call your helpers besides Allah, if you are truthful. (Al-Baqarah 2:23)
Faʾtū bi-sūratin min mithlihī presents the Qur’an’s challenge as evidence of its miraculous nature. Because the Qur’an is still present, the challenge remains.
Those who lived at the time of revelation and those who come afterward can both encounter this evidence for the Prophet’s truth.