﴿ وَإِنَّهُۥ لَحَسْرَةٌ عَلَى ٱلْكَٰفِرِينَ ﴾

“yet, behold, this [rejection] will indeed become a source of bitter regret for all who deny the truth [of God's revelation] –”

And assuredly it that is the Qur’ān is a cause of anguish for the disbelievers when they see the reward of those who affirmed its truth and the punishment of those who denied it.