Surah Fussilat 33
And who is better in speech than one who invites to Allah and does righteousness and says, "Indeed, I am of the Muslims."
Surah An’aam 159
Indeed, those who have divided their religion and become sects - you, [O Muhammad], are not [associated] with them in anything. Their affair is only to Allah ; then He will inform them about what they used to do.
Surah Al Imran 103
And hold firmly to the rope of Allah all together and do not become divided.