How do I prove Allah’s singularity?

Tawhid is the indivisible oneness concept of monotheism in Islam. Tawhid is the religion's central and single most important concept, upon which a Muslim's entire religious adherence rests. It unequivocally holds that God as per Islam is One and Single.

Tawhid constitutes the foremost article of the Muslim profession of submission. The first part of the shahada or testimony (the Islamic declaration of faith) is the declaration of belief in the oneness of God. To attribute divinity to anything or anyone else, is shirk – an unpardonable sin according to the Qur'an, if repentance is not sought afterwards. Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid.

Allahu ta’âlâ’s existence and oneness were proven through scientific and mental evidences as well. The scholars of Kalâm, by seeing “the effect” through mental evidences, inferred the cause from the effect. The Hukamâ [that is, the scholars who have both religious and scientific knowledge], through scientific evidences, saw the power of the cause and deduced that this power is the cause of all beings. Some of the proofs that show the existence and oneness of Allahu ta’âlâ are as follows:
1. It is purported in an âyat-i karîma:
(If there were gods besides Allahu ta’âlâ on earth and in the heavens, order in these places would have become deranged and a complete disorder would have prevailed.) [Sûrat-ul-Anbiyâ’, 22]

This âyat-i-karîma signifies the following:
Supposing the universe had two creators; the courses of action chosen by these two creators would be either disparate or identical. If they were disparate, then the universe would get into mischief. That is, the heavens and earth would be thrown into disorder and perish, or two contradictory things would coexist. For instance, if one of the two gods wished a certain person to move and the other god wished him or her not to move, when their godly powers affected this person, two opposite things would happen at the same time. And this, in its turn, is impossible. In other words, it is impossible for two opposite events to take place at the same time. That is, this person cannot be both moving and not moving at the same time. (S)he is either moving or not moving.

If the courses of action chosen by the two gods were not identical, for example, if one of them said “This action should be in this way” and if the other said “No, it should be in that way ,” in the end, if one of them overwhelmed the other, then one of them would necessarily be powerless. And being powerless, in its turn, would mean being a creature, having been created afterwards, which would be incompatible with the honor of being a god. Something created afterwards could not be a god.

2. Supposing the universe had two creators, [may Allahu ta’âlâ protect us from saying so], either one of them would be either capable, or incapable, of doing whatever he wished to do. If one of them were sufficiently capable of doing whatever he wished to do, the second god would be null and void, nonessential and superfluous, which would mean imperfection. And he who were imperfect, in turn, could not be a god. If the second god were sufficient to do whatever he wished to do, this time the first god would become null and void or âtil. Can an âtil thing be a god? Âtil means good-for-nothing, useless.

3. Supposing the universe had two creators, they would either need each other, or not. Or one of them would need the other, and the latter in turn would not need the former. In the first case, i.e. if they both needed each other, they would necessarily be imperfect. In the second case, that is, if they did not need each other, neither would be a god. For each would be nonessential and superfluous in comparison with the other, which would be incompatible with a godly character. For a god must be an all-inclusive being whom everything needs every moment. Not needing him, therefore, would be out of the question. In the third case, the one that needed the other would normally be imperfect, which would mean only the latter one were a god, and hence only one god.

There is absolutely One Creator of this universe. He decreed to create the universe and did create it. Nothing would have existed if He had not decreed and created it. Nothing can come into existence by itself. There is definitely a Creator of everything. A pen cannot write by itself. It certainly needs an agent to make it write. And this agent, as everyone knows, is the writer. As it would be impossible for a pen to write without a writer, so would it be impossible for the universe to exist without a Creator.

4. Supposing the universe had two creators and one of these creators wanted a person to stand up and the other god wanted him to sit down. This person would either stand up or sit down; either case is possible. But when both gods’ wishes took effect at the same time, this one would have to both stand and sit at the same time. And this, in its turn, would mean to make two opposite things one, which is impossible. If only what one of them wished were to happen, then the other would be incapable. It is out of the question for a god to be incapable, for incapability is peculiar to creatures. On the other hand, it is impossible for a creature to have existed since eternity. As eternal incapability is impossible, so it is impossible for a god to be incapable or of recent occurrence. If it were impossible for the other god to will that this person should sit down, this would mean that one of them outacted the other’s will, which, in turn, would mean the other’s incapability. And he who is incapable could not be a god.

Beings existing in the universe cannot come into existence or cease to exist from themselves. There is a being who effects, creates them. Since there are worlds, and creatures in these worlds, there is a Being who creates these worlds and the creatures in these worlds. Existence of creatures is an evidence for the existence of a Creator, and this Creator is Allahu ta’âlâ. Creatures in the universe have attributes. Then, Allahu ta’âlâ, who creates them, has these attributes.

There was nothing in the universe. Allahu ta’âlâ created them all. All of them are recent occurrence. That is, they may come into existence from nonexistence or cease to exist, and they came into existence from nonexistence. The hadîth-i sharîf, “Allahu ta’âlâ was existent, anything else did not exist,” expresses this fact.

Another proof evincing that the universe is of recent occurrence is the fact that the universe is subject to a continuous process of changing. Everything is changing. What is eternal, on the other hand, will never change. Allahu ta’âlâ Himself and His Attributes never change. In the universe, on the contrary, physical changes take place in substances, and chemical reactions change essence, construction of matter. We see objects’ ceasing to exist and changing into other objects. According to recent findings, atomic changes and nuclear reactions cause substances and elements to cease to exist and turn into energy. These changes in ’âlams and substances and their coming into being from one another could not be happening since eternity. They must have a beginning, a first set of substances and elements that were created from nothing and from which they came into being.

Another evidence to prove that the universe is dispensable, that is, that it may come into being from nothing, is the fact that the universe is of recent occurrence. In fact, we see that all things around us have come into existence from nothing. Things are ceasing to exist. Other things are coming into existence from them. However, according to our latest chemical knowledge, the hundred and five elements never cease to exist in chemical reactions. Only their constructions change. Radioactive events have shown that elements, and even atoms, cease to exist and that matter changes into energy. As a matter of fact, the German physicist named Einstein has formulated this change mathematically.

This continuous process of changes in substances and their coming into being from one another must not be coming from eternity. It could not be said that it has always been this way and it will always be. These changes have a beginning. To say that the changes have a beginning means to say that the existence of substances has a beginning. It means to say that all beings were nonexistent and were created from nothing afterwards. If the first substances had not been created from nothing, if their coming into being from one another went back into eternity, this universe would necessarily be nonexistent today. For beings’ coming into existence from one another in eternity would require preexistence of other beings to give birth to them, and these other beings’ existence would require yet other beings’ existence before them. Existence of later ones would depend on the existence of earlier ones. If earlier ones did not exist, later ones would not exist, either. Eternal means without beginning. A being’s coming into existence from nothing in eternity would mean that there were not a first being. And if the first being did not exist, there could not be any beings later. As a result, everything would necessarily be always nonexistent. There could not be an endless chain of beings, each of which would need another being previous to it for its existence. All of them would necessarily be nonexistent.

The fact that the universe exists now shows that it has not existed since eternity in the past and that there was a first being created from nothing. It is necessary to believe that the universe has been created from nothing and that today’s universe has been formed after successive chains of things coming into being from one another since that first being.

There are two sorts of existence: First, things that are created afterwards (creatures); second, the One who is the Ever-existing (Wâjib). If the only type of existence were the creatures and the Wâjib-ul-wujûd (indispensable being) did not exist, then nothing would exist. For it is a change, an event, to come into existence from nothing. According to our knowledge of physics, in order for a change to take place in a substance, the substance has to be acted upon by an exterior power, the source of which has to precede the substance. Therefore, a created thing could not come into existence or maintain its existence by itself. If some power did not effect it, it would always remain nonexistent; it could never exist. Something which could not create itself, could not create others, either. Creator of the creatures has to be the Wâjib-ul-wujûd (indispensable being). Existence of the universe shows that there is a Creator who created it from nothing.

As it is seen, the only Creator of all dispensable beings is Allahu ta’âlâ, who is the only Wâjib-ul-wujûd, and who is not of recent occurrence or dispensable.

Wâjib-ul-wujûd means that its existence is indispensably necessary. It means “Being whose existence does not depend on someone or something else and who eternally exists only by itself.” He is not created by someone else. Were it not so, He would necessarily be dispensable and of recent occurrence and someone else’s creature. A creature, on the hand, cannot be a god. In Persian Khudâ’ means “always self-existent, eternal.” (Imâm-i Râzî, Qâdî Baydâwî)