Surely Allah is not ashamed to set forth any parable-- (that of) a gnat or any thing above that; then as for those who believe, they know that it is the truth from their Lord, and as for those who disbelieve, they say: What is it that Allah means by this parable: He causes many to err by it and many He leads aright by it! but He does not cause to err by it (any) except the transgressors,

And We have not made the wardens of the fire others than angels, and We have not made their number but as a trial for those who disbelieve, that those who have been given the book may be certain and those who believe may increase in faith, and those who have been given the book and the believers may not doubt, and that those in whose hearts is a disease and the unbelievers may say: What does Allah mean by this parable? Thus does Allah make err whom He pleases, and He guides whom He pleases, and none knows the hosts of your Lord but He Himself; and this is naught but a reminder to the mortals.