the Christians say, ‘The Jews have no foundation.’”
[Surah al-Baqarah 113]

And Allah Most High says:

“Do you then believe in part of the Scripture and disbelieve in part?”
[Surah al-Baqarah 85]

And Allah Most High says:

“And do not be like those who became divided and differed after clear proofs had come to them.”
[Surah Āl ʿImrān 105]

And Allah Most High says:

“Indeed, those who have divided their religion and become sects—you have nothing to do with them.”
[Surah al-Anʿām 159]

As for Allah’s religion and guidance, with which He sent down His Book and sent His Messenger, it consists in following His Book and His Messenger’s Sunnah in all matters, refraining from following anything contrary to them in any matter, and being united upon this.

As Allah Most High says:

“O you who believe, fear Allah as He should be feared, and do not die except as Muslims. And hold firmly to the rope of Allah all together and do not become divided. And remember Allah’s favour upon you: when you were enemies, He brought your hearts together, and by His favour you became brothers. You were on the brink of a pit of Fire, and He saved you from it. Thus Allah makes His signs clear to you so that you may be guided.

“And let there be among you a group calling to good, enjoining what is right and forbidding what is wrong. It is they who will be successful. And do not be like those who became divided and differed after clear proofs had come to them. For them there will be a tremendous punishment on the Day when some faces will turn white and some faces will turn black. As for those whose faces turn black: ‘Did you disbelieve after having believed? Then taste the punishment for your disbelief.’ But as for those whose faces turn white, they will be within Allah’s mercy,