One day an atheist from Egypt came to Imam (a.s) who asked his name. “Abdul Malik,” replied he. Imam (a.s) asked what his agnomen was. “Abu Abdullah,” he replied. Imam: The kingdom whose slave you are, is it from the kingdom of the heavens or from the kingdoms of the earth? Atheist: I have never reflected on it. Imam: Have you ever gone below the earth’s surface? Atheist: No. Imam: Do you know what is below it? Atheist: I have no knowledge of it. Imam: Have you ever ascended to the sky? Atheist: No.
Imam: Do you know what exists there? Atheist: No. Imam: Have you visited east and west? Do you know what lies beyond the limits? Atheist: No.
Imam: It is surprising that when you do not have any knowledge about the earth or the sky, the east or west, how can you deny the existence of God? How can an ignorant man make such a great claim? Just ponder upon it; the moon, the sun, the night and the day, which all move in a particular way, are they not helpless and captive in their orbits? If they had not been so, they would not have returned after passing away once. If they are not helpless, why is it not that sometimes there is night instead of day? Don’t you ever reflect on the earth and the sky that why the sky does not crash on the earth? Why the earth does not sink below itself? Who has made them stable? One who has done this is our and their absolute powerful God.” Hearing these words, he was astonished and at that very moment recited the dual testimony of Islamic faith and became a Muslim.
Reference :Akhlaq al-A’imma, Morals & Manners of the Holy Imams