Shaykh al-Islām Taqī al-Dīn was asked:

Concerning those who claim to believe in Allah, Mighty and Majestic, His angels, His Books, His messengers and the Last Day, yet believe that the rightful imam after the Messenger of Allah, may Allah bless him and grant him peace, was ‘Alī ibn Abī Tālib; that the Messenger of Allah, may Allah bless him and grant him peace, explicitly designated him as imam; and that the Companions wronged him, denied him his right and thereby became disbelievers: is it obligatory to fight them? Does this belief make them disbelievers or not?

He replied:

All praise belongs to Allah, Lord of all worlds. Muslim scholars unanimously agree that any group that resists compliance with any of Islam’s manifest ordinances established through mass transmission must be fought until all worship is devoted to Allah alone.

Thus, if they were to say: “We pray but do not pay zakat”; or, “We perform the five daily prayers but do not perform the Friday prayer or pray in congregation”; or, “We uphold the five pillars of Islam but do not regard Muslims’ blood and property as inviolable”; or, “We will not give up usury, intoxicants or gambling”; or, “We follow the Quran but do not follow the Messenger of Allah, may Allah bless him and grant him peace, or act upon the hadiths reliably established from him”; or, “We believe that Jews and Christians are better than the general body of Muslims, and that those who face the qiblah have disbelieved in Allah and His Messenger, with only a small group of believers remaining among them”