How should one deal with Muslims who hold different beliefs, such as those who deny God's attributes, or Shiites who declare Abu Bakr and Umar to be infidels, especially if they do not respond to advice? Is it permissible to pray behind them or with them, or should one continue to interact with them only in worldly matters?

It is recommended to derive Islam and creed from the Qur’an and Sunnah (definition), and from the books of the righteous predecessors of the Ummah, specifically the books on creed written by scholars who were not biased towards any particular sect, such as Kitab as-Sunnah by Imam Ahmad and his son, and Kitab al-Iman by Ibn Abi Shaybah. Creeds that deny the attributes of Allah (such as the Hand), or claim that Allah is everywhere, or declare the Companions to be disbelievers, are innovative. One should avoid those who hold such creeds if they are not convinced [otherwise], and attempt to persuade them with books on the Salafi creed and books refuting the misconceptions of innovators, such as the works of Uthman ibn Sa'id ad-Darimi. If they are not convinced, then one should not pray behind them, and should seek those who adhere to the Salafi creed.