Ar-Raib: It is the doubt. This is actually a Divine challenge, as Allah U says to mankind:

﴾وَإِنْ كُنتُمْ فِي رَيْبٍ مِمَّا نَزَّلْنَا عَلَى عَبْدِنَا فَأْتُوا﴿ “And if you are in doubt about what We have sent down upon Our Servant, then produce”. Allah U has sent down the Holy Qur’an from the Lauh Mahfuz to the House of Honour in the nearest heaven all at once in Laylatul Qadr (Night of Decree) in the month of Ramadan, as He U tells us:

﴾شَهْرُ رَمَضَانَ الَّذِي أُنزِلَ فِيهِ الْقُرْآنُ﴿

“The month of Ramadhan [is that] in which was revealed the Qur’an” [Surah Al-Baqarah: 185] and

﴾إِنَّا أَنزَلْنَاهُ فِي لَيْلَةِ الْقَدْرِ﴿

“Indeed, We sent the Qur’an down during the Night of Decree.

”[Surah Al-Qadr: 1].

The phrase ﴾عَلَى عَبْدِنَا﴿ “upon Our Servant” is referring to the Prophet r, as an honour for him.