Imam Sadiq (as) debate with Abu Shakir al-Daysani

Abu Shakir al-Daysani, an atheist, came in to Imam al-Sadiq, peace be on him, and said to him:
-O Ja‘far b. Muhammed, show me the way to the One Whom should I worship!
Abu ‘Abd Allah said:
-Sit down!
A boy came. The boy was carrying an egg in the palm of his hand. The Imam, peace be on him, ordered him to hand him the egg, and he handed it to him. Then he, peace be on him, said:
-O Daysani, this is a compact, protective container; inside it is the thin (substance of an) egg which is surrounded by what could be compared with fluid silver and melted gold. Neither the fluid silver mixes with the melted gold; nor does the melted gold mixes with the fluid silver. So it is as it is. No reforming exterior comes out of it and tells (you) about its goodness, nor does a corrupt interior comes into it and tells you about its corruption. None knows that it has been created for a male or a female. Then it splits open showing a form like (for example) a peacock. Therefore, do you think that it has a Creator?”
Al-Daysani bowed his head and thought about the Imam’s words. Shortly after that, he raised his head and said: “I bear witness that there is no god but Allah, the One without a partner; and I bear witness that Muhammed is His Servant and Apostle. I bear witness that you are an Imam and Allah’s proof over His creatures. I have repented of what I had believed in!” ( Al-Ihtijajj.)