This is set out in three verses:

The first is His statement, Most High:

“Had there been in the heavens and the earth gods besides Allah, both would have fallen into ruin.” [al-Anbiyā’: 22]

The second is His statement:

“Allah has never taken a son, nor is there any god alongside Him. Otherwise, each god would have taken away what he created, and some would have overpowered others. Exalted is Allah above what they ascribe to Him.” [al-Mu’minūn: 91]

The third is His statement:

“Say: If there were gods alongside Him, as they claim, they would have sought a way to the Lord of the Throne.” [al-Isrā’: 42]

As for the first verse, its argument is naturally ingrained in human nature. It is self-evident that if there were two kings, each performing the same kind of action as the other, a single city could not be governed by them both. For a single act cannot proceed from two agents of the same kind. Thus, if they acted together, the city would necessarily fall into ruin—unless one acted while the other remained inactive, which is incompatible with divinity. Whenever two actions of the same kind converge upon the same object, that object is necessarily ruined, or the actions thwart one another; for a single act can proceed only from a single agent.

This, then, is the meaning of His statement, glorified is He:

“Had there been in the heavens and the earth gods besides Allah, both would have fallen into ruin.” [al-Anbiyā’: 22]