My question is about Shi`a and Qadianiyyah. They don�t believe in some pillar of Islam. Are they Muslims?
In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
As far as the moderate Shi`ah like Ithna �Ashriya or Imamiyyah are concerned, generally they have been accepted as Muslims by the Ijma� (juristic unanimity) of the Muslim community and that is why they have been permitted to go for hajj while it a recognized fact that non-Muslims are not allowed to perform hajj.
This Ijma� of the community does not apply to people who have violated the fundamental principles of Islam, such as those who prophesied the divinity of �Ali, may Allah be pleased with him, or denied the fact that prophethood has ended with Prophet Muhammad, peace and blessings be upon him.
As for Qadianis, they have violated these principles when they claimed that Mirza Ghulam Ahmad is a prophet. Due to this violation, they cannot be called Muslims and this has also been established by the Ijma� (concensus) of Muslims.