Question:

Are the Bori Shias outside the fold of Islam? Why? Is it allowed to say salam to them? If they say salam, then how should we reply to them?

Answer:

There are many sects of the Shias. Some are kafir (non-believers). For instance, those who believe in the god-ship of Ali رضي الله عنه; or are of the belief of hulool (pantheism); or believe there was an error in whom the revelation was to be brought to; or they slander Aishah Siddiqah رضي الله عنها; or they believe in parts of the Quran missing or parts being added to it. (Kifayatul Mufti 1/286) This is because all the above beliefs necessitate denying qat’i mutawatir nusoos (categorical textual evidences). This is why there are considered kafir. One should not say salam to them. If they say salam, then reply with: “وعليكم” (And upon you) or with “هداك الله” (May Allah guide you). (Fatawa Mahmudiyah 5/221)

And Allah Ta’ala knows best.
(Hazrat Mufti) Ahmed Khanpuri (May Allah protect him)
Mahmoodul Fatawa Vol.4 Pg.710