It is narrated from Sayyiduna Abu Malik al-Ash'ari (may Allah be pleased with him) that he heard the Messenger of Allah (peace and blessings be upon him) say: "There are three things that I have hidden from My servants; if they saw them, they would never do any evil: if I were to lift My veil so that he saw Me in such a way that he became certain and knew what I do with My creation when I cause them to die and grasp the heavens in My Hand, then grasp the earth and the earths, then say: I am the King; who is there who has dominion besides Me? Then that I show them Paradise and all the good I have prepared for them in it, so that they become certain of it; and that I show them the Fire and all the evil I have prepared for them in it, so that they become certain of it. But I have deliberately hidden this from them, so that I may know how they act, even though I have made it clear to them."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 3434