Tafsir of Al-An'am 6:148-149

{Those who associated partners will say} This is a foretelling of what they would say. When they actually said it, He said: “And those who associated partners said: ‘If Allah had willed, we would not have worshipped anything other than Him’” (al-Naḥl: 35). They meant by their disbelief and rebellion that their polytheism, the polytheism of their forefathers, and their forbidding of what Allah had permitted were all by the will and desire of Allah. They argued that were it not for His will, none of that would have occurred—which is precisely the doctrine of the Mujbira (determinists).

{Likewise did those before them deny} Meaning: They brought forth absolute denial. This is because Allah, the Almighty and Majestic, has instilled in the intellects and revealed in the Scriptures that which proves His transcendence above willing or desiring abominations, and the Messengers have informed [people] of this. Therefore, whoever attributes the existence of abominations—such as disbelief and acts of disobedience—to the will and desire of Allah has denied everything; it is a denial of Allah, His Books, and His Messengers, and a casting of the proofs of reason and revelation behind their backs.

{Until they tasted Our punishment} Until We sent down upon them the torment for their denial.

{Say: "Do you have any knowledge?"} Any known matter that is valid to use as an argument for what you have said.

{That you can bring forth for us?} This is a form of mockery, testifying that it is impossible for a claim like theirs to have any proof.

{You follow nothing but conjecture} In this statement of yours.

{And you are nothing but liars} You estimate that the matter is as you claim, or you are simply lying. It has also been recited as kadhaba (denied) with a light dhal (instead of kadhdhaba).

{Say: "To Allah belongs the conclusive argument"} Meaning: If the matter were as you claimed—that what you are upon is by the will of Allah—then to Allah belongs the conclusive argument against you, according to the logic of your own doctrine.

{For had He willed, He would have guided you all} Both you and those who differ with you in religion. For your attributing your religion to the will of Allah necessitates that you also attribute the religion of those who differ with you to His will. Thus, you should befriend them rather than show them enmity, and agree with them rather than oppose them, because the [divine] will encompasses both what you are upon and what they are upon.

{Say: "Bring forward your witnesses who testify that Allah has forbidden this." Then if they testify, do not testify with them, and do not follow the desires of those who denied Our signs and those who do not believe in the Hereafter, while they equate others with their Lord.}