If I'm in a debate with an atheist and then it comes to the point when he says "Then who created God?", how should my response or answer be?
In the name of God, the Most Gracious, the Most Merciful.
Atheists tend to ask this question to Muslims. "Who created God"?
God is the first, with no beginning, and the last, but with no ending. So the answer is that God was never created in the first place. He was there. That's it. Here's a video that will explain this: https://www.youtube.com/watch?v=-zVpw2-OD4M
Fully accepting the oneness of God is to accept that He is distinct from everything else. It would not suit God’s majesty and glory to associate the limited attributes of His creation to Him because He is not restricted in any way, while His creation is. He is the First with no beginning and the Last with no end. Everything in the universe was created by His will. He is not confined by space or time and He is the only One who is in control and provides for His creation.
That site will also help you on this regard, and how to talk to atheists in general.
I really hope this helps, and Allah knows best.
Peace be unto you.
As salamu Alaikoom
Now, I'm going to take a very logical, perhaps even a philosophical point of view to this question.
When we look at the existence of God - the immaterial and only god we have only three possibilities:
1) God was created
2) God created himself
3) God was not created and always existed.
1) God was created.
So if we state "God was created" (Astaghfirullah) then we can say "A God (being/entity) created Allah who created the universe." However, a problem arises, we can now ask, "Well, who created the entity who created God Who created the universe?" and even then we can ask, "Who created the God who created the God who created the universe?" and even then we can ask, "Who created the God who..." and this question goes on for infinity.
This infinite regression is called infinite regress and infinite regress is impossible - you cannot have an infinite amount of past events otherwise you will never reach the present.
So in reality, the possibility of Allah being created does not make sense so this possibility must be over-ruled.
To demonstrate further how this possibility is wrong, let me give you an example:
Imagine I ask you "can I see your cat." However, you reply, "ask my mother." Then I ask your mother, "can I see your cat" and even then she replies "ask my mother". Then I ask your grandmother the same question and likewise she replies, "ask my mother." And this chain continues for an infinte past so will I ever get to see your cat? NO.
Therefore, this possibility is wrong - now the next possibility:
2) God created Himself
This is completely absurd - this is like stating, "my mother gave birth to herself" This we all know is quite impossible - one cannot be in a state of existence and non-existence at the same time - these two states are completely mutually exclusive.
now the last possibility:
3) God has always existed
This is the only logical stance when it comes to the existence of God and by the principle of Occam's Razor this is the best explanation
Occam's Razor - the simplest explanation is the best explanation.
Now just because, we of our limited nature, cannot comprehend how Allah has always existed we just have to accept that Allah has. Similarly, the fact that this is the best explanation does not mean now that this explanation needs a further explanation - this is also compatible with science - we don't have an infinite amount of tests to prove something is true or not - we have a finite amount of tests in which we conclude from our results and then we let it be.
Allah tells us that he is Al- Awwal (The first) and what comes before 1? Zero right? So nothing comes before Allah but Allah is the first (and only) being who was always in existence. Allah was even before "before" - Allah is not limited to time, Allah created time! Subhanallah!
"Say, "He is Allah, [who is] One
Allah, the Eternal Refuge.
He neither begets nor is born,
Nor is there to Him any equivalent."
In reality, the whole question "Who created God?" is an invalid question so explain to them these three possibilities and show how the answer must be that Allah was not created but he has always existed.
Hope that helped insha'allah! Salaam.
Not that we can define God, but we know some of its attributes.
I think what you should do first is define what God is. when we say الله الصمد it means God doesn't need ANYTHING. ( don't read the verse to him but convey the message :D )
Whatever that is in need is created and therefore weak. There is only 1 entity in this world that is not in need and that is Allah.
Having that said. Depending on your situation. I recommend never ever engage in a discussion when one is not asking but rather making statements. Did this person come to asking about God or did you go to him assert your ideology?
If he comes to you then give him all you got. The moment you see him saying nonsense then that's the moment where you stop the discussion and not proceed.
In addition don't make statements. Ask him questions. Don't say There is a God. Ask him how do you think this universe was created. Keep asking questions until you see either his fitra (فطره) comes out, or you see him conceal کفر his fitra.