Al-Baqarah - 2:26

إِنَّ اللَّهَ لاَ يَسْتَحْيِي أَن يَضْرِبَ مَثَلاً مَّا بَعُوضَةً فَمَا فَوْقَهَا فَأَمَّا الَّذِينَ آمَنُواْ فَيَعْلَمُونَ أَنَّهُ الْحَقُّ مِن رَّبِّهِمْ وَأَمَّا الَّذِينَ كَفَرُواْ فَيَقُولُونَ مَاذَا أَرَادَ اللَّهُ بِهَـذَا مَثَلاً يُضِلُّ بِهِ كَثِيراً وَيَهْدِي بِهِ كَثِيراً وَمَا يُضِلُّ بِهِ إِلاَّ الْفَاسِقِينَ
[2:26]
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,
Allah disdains not to use the similitude of things, lowest as well as highest. Those who believe know that it is truth from their Lord; but those who reject Faith say: "What means Allah by this similitude?" By it He causes many to stray, and many He leads into the right path; but He causes not to stray, except those who forsake (the path),-
Lo! Allah disdaineth not to coin the similitude even of a gnat. Those who believe know that it is the truth from their Lord; but those who disbelieve say: What doth Allah wish (to teach) by such a similitude? He misleadeth many thereby, and He guideth many thereby; and He misleadeth thereby only miscreants;