Gai Eaton writes in his book on Eastern Wisdom ‘The Richest Vein’ (written before he became Muslim I believe):

‘According to the Islamic teaching, each sphere of Hell offers to it’s inmates a pleasure to which they become attached, for if they suffered nothing but agony they would call upon the Mercy of Allah, and that Mercy could not be denied them’.

I found this to be profoundly moving as an illustration of the mercy of Allah. Has anyone else heard of this?