These passages from the Quran make clear that those who differed did not do so until knowledge and clear proofs had come to them. They differed out of transgression and wrongdoing, not because truth and falsehood had become confused in their minds. This is the condition of all who engage in blameworthy disagreement among the people of caprice: they differ only after the truth has become clear to them(1) and knowledge(2) has come to them, whereupon they transgress against one another. Moreover, among those engaged in blameworthy disagreement, each transgresses against the other: he rejects the truth the other possesses, even though he knows it is true, and affirms the falsehood he himself holds, while knowing(3) it is false.

All such people are blameworthy. This is why all those engaged in unrestricted disagreement(4) are condemned in the Book and the Sunnah, for every one of them rejects some truth and follows some falsehood. Allah therefore commanded the messengers to call people to one religion—the religion of Islam—and not to become divided therein. It is the religion of the earlier and later messengers and their followers.

Allah Most High said:

“He has ordained for you the same religion that He enjoined upon Noah, that which We have revealed to you, and that which We enjoined upon Abraham, Moses, and Jesus: uphold the religion and do not become divided therein. What you call the polytheists to is grievous to them.”

[Surah al-Shūrā: 13]

In another verse, He said:

“O messengers, eat of the wholesome things and do righteous deeds. Indeed, I know well what you do. This community of yours is one community, and I am your Lord, so fear Me. But they divided their affair among themselves into separate writings, each faction rejoicing in what it possessed.”

[Surah al-Mu’minūn: 51–53]