According to the teachings of prophets, there is only one true God Who is All-Powerful, and Who is the Creator and Sustainer of the universe. This one God has many names; however, Muslims mostly refer to this only true God as Allah. Some other names for Allah are mentioned later on this website. 

Monotheism is the core belief of Islam. Muslims believe in one God Allah Who is indivisible and incomparable to any other being. He has no partners in His divinity. Allah SWT neither begot anyone nor was He begotten. Surah Ikhlas in the Holy Quran briefly describes these qualities of Allah SWT in the following verses:

Thus, unlike Christianity, Islam does not believe that God has a son. Muslims consider Jesus (Prophet Esa AS) as one of the greatest prophets of God. However, Jesus (Prophet Esa AS) himself never proclaimed his divinity, and the concept of trinity was later introduced by some people. Ayat-ul-Kursi which is one of the most famous verses of the Holy Quran mentions Allah SWT (true one God) in the following words: 

As per the teachings of prophets, God in Islam is understood as an eternal being Who has always existed and will always exist. There is no concept of creation in the existence of God as He is eternal. He was never created and is beyond time and space. Creation would imply His dependency on other factors for His existence. This is not true as Allah SWT is not dependent on anything as He is “… Besought of all, needing none.” (Surah Ikhlas, Ayat 2). Nothing other than God is eternal including the matter and the soul. Everything else was created and has a finite existence.  In Islam, God is seen as beyond human comprehension therefore it is impossible to fully understand Allah SWT.

Islam strongly emphasizes the oneness of God. Otherwise, the existence of many powerful gods in the universe would have resulted in disagreements among the gods in the design, creation, or functioning of the universe. Therefore, either the universe could have not been created in the first place or its system must have collapsed at the later stages due to the likely tug-of-war of various authoritative gods in the universe. For example, both Greek and Hindu mythologies thunder with tales of epic battles between their gods, each wielding power both awe-inspiring and destructive. The following verses of the Holy Quran assert that there would have been a massive disorder in the universe if there were more than one God: 

“Allah has not taken a son to Himself, nor was there any god with Him. Had there been so, every god would have taken away what he created, and each one of them would have been aggressive against the other. Pure is Allah from what they describe.” (Surah Mominun, Ayat 91). 

“Say, had there been other gods along with Him, as they say, then they would have found out a way to the Lord of the Throne.” (Surah Bani Israel, Ayat 42).

“Had there been gods beside Allah, in the heavens and the earth, both of them would have fallen in disorder. So pure is Allah, the Lord of the Throne, from what they describe.” (Surah Anbiya, Ayat 22). 

However, instead of disorder, we see complete order in the universe as mentioned in the following verses of the Holy Quran, “… You will see nothing out of proportion in the creation of the Rahman (the All-Merciful Allah). So, cast your eye again. Do you see any rifts? Then cast your eye again and again, and the eye will come back to you abased, in a state of weariness.” (Surah Mulk, Ayat 3 & 4). 

Thus, Muslims believe in only one God Who is the Creator and Sustainer of the universe and is All-Powerful. Associating anything or anyone with Allah SWT (God) in terms of His divinity, lordship, or worship is considered the gravest sin in Islam as it negates the core principle of monotheism. This sin is known in Arabic as “shirk” that can take many forms including attributing the creation, ownership, or control of the universe to anyone other than Allah SWT. This grave sin also includes praying or worshipping anyone or anything besides Allah SWT, including idols, prophets, saints, graves of pious people, or nature.