This tale is perhaps the most understandable, indisputable and convincing about the existance of God. It goes like this:
An atheist asked Imam Ja’far as-Sadiq (as),how could he convince him about the existence of God. Coming to know that the man had gone several times on sea voyages, Imam asked him “Have you ever been caught in a fierce storm in middle of nowhere, your rudder gone, your sails torn away, trying desperately to keep your boat afloat?” The answer was `Yes’. Then Imam asked: “And sometimes perhaps even that leaking boat went down leaving you exhausted and helpless on the mercy of raging waves?”
The answer was again `Yes’.
Then Imam asked: “Was not there, in all that black despair, a glimmer of hope in your heart that some unnamed and unknown power could still save you?” When he agreed, Imam said: “That power is God.”
That atheist was intelligent. He knew the truth when he saw it.
Good to know:
Imam Jafar Sadiq (as) is the 6th descendent of the Prophet (p.b.u.h). He is teacher to notable personalities in history such as Jabir Bin Hayyan, Imam Malik and Imam abu Hanifa
P.S : Although I have heard this tale in person from a great scholar, but right now I’ve copied it from http://www.al-islam.org/god-an-islamic-perspective/3.htm
A man once came to Imam Ali (A.S.) requesting for proof on the existence of God. In response the Imam said, “The waste balls of a camel prove its existence and the dung of a donkey proves its existence and the footprints are evidence that someone passed a certain way. So why should not this sky and earth serve as the evidence, of the existence of One most Great and All-knowing.”