The Quran

فَلَمّا نَسوا ما ذُكِّروا بِهِ فَتَحنا عَلَيهِم أَبوابَ كُلِّ شَيءٍ حَتّىٰ إِذا فَرِحوا بِما أوتوا أَخَذناهُم بَغتَةً فَإِذا هُم مُبلِسونَ

Muhammad Asad

Then, when they had forgotten all that they had been told to take to heart, We threw open to them the gates of all [good] things,¹ until - even as they were rejoicing in what they had been granted - We suddenly took them to task: and lo! they were broken in spirit;²

I.e., to test them by happiness after the test by misery.
The verb ablasa signifies "he despaired of all hope" or "became broken in spirit". (For the linguistic connection of this word with the name of Iblis, the Fallen Angel, see Sarah 7, note 10.)