I was returning a book to McMaster University's library when I ran into A--- at the Muslim Student Association booth, who offered to answer any question on Islam, "no matter how controversial." I was impressed with this young proponent of his Faith. I asked for an essay about Muslim proofs of deity, the subject of a talk I was preparing. A colleague of his emailed me the following, which I share here with permission.
So in terms of proving the existence of God in Islam we use two things: the Quran and the life and teachings of the Prophet Muhammad (peace be upon him). These are the two things that show us that there is a God and that he is communicating with humankind. The Quran very rarely will address the existence of God because it is already assumed that God exists since it is the speech of God. Imagine, for instance, having a conversation with someone - they wouldn't need to tell you that they exist because that conversation entails that they exist.
You might now ask, well how do we know that the Quran is the speech of God?
The answer to that is its miraculous nature: its inimitable language, it's historical, scientific, and linguistic miracles. For a better idea on the miraculous nature of the Quran please watch the following video by a renowned Muslim scholar, Yasir Qadhi. He starts at 4:10 and continues on to talk about how the Quran is miraculous.
The second way we prove the existence of God is by reflecting on the life and teachings of the messenger. God sent us many messengers to remind us of our duty to worship Him and the Prophet Muhammad (peace be upon him) was the last and final messenger.
How do we know that he was a true messenger of God? We can easily deduce this with the following options: either he was a liar, he was deluded, or he was a true messenger.
Now he couldn't have been a liar because he was known as the honest and trustworthy of his people even before he became a Messenger (at age 40). People would keep their gold and precious belongings with him whenever they went on a journey. And he would always return it to them, thus he was a very honest person.
It could also be argued that he wanted to be a messenger for money and power. But if you look at his life you can see that this was not the case. When he first started calling people to Islam the tribe leaders tried to persuade him to stop. So they offered him riches, women, power but his reply was
“By God! If they were to place the sun in my right hand and the moon in my left hand in order to abandon this mission, I would not do so until it has been well established or I would perish in my attempt to do so.”
This, along with many other examples, proves that he was not in it for worldly desires.
Then was he deluded? Well, he was not known to be insane his whole life, but rather was known as the man with the best character. It is extremely rare to develop a psychological disease when you are 40 without showing any signs during upbringing.
Additionally, the insane have difficulty having a conversation one on one let alone be the leader of a political, social, cultural, and religious revolution that changed the face of human history. Another point is that the Quran is very eloquent and consistent so it is impossible for such a coherent message with a clear system of guidance and set of laws for all aspects of life to be produced by someone who is not mentally stable. You can watch the following video by another Muslim scholar, AbdulRaheem Green to get a better idea:
So this is basically the Islamic way of proving the existence of God - His Message (the Quran) and His Messenger (Muhammad). If you have any other questions feel free to contact me and I would be more than happy to help!
Thanks for your interest!
--- Muslim Students Association