Bahá’ís Cannot Associate with Those Who Have Left the Cause and are Associating with Covenant-Breakers

"There is no excuse for believers continuing to associate with … and those who, knowing everything, still insist on doing so, should be shunned by their fellow-Bahá’ís. The same applies to people who have left the Cause and associate with …. The point is that if the believers know and meet with people who are acquainted with Covenant-breakers there is no harm in this, for such individuals are not Bahá’ís and have nothing to do with the issues concerned. But those who have left the Cause, knowing all about such matters, and deliberately associate with Covenant-breakers, are well aware of what they do, and we must not associate with them at all. It is for the Local Assembly, guided by the N.S.A., to enforce such decisions and protect the Cause in its area of jurisdiction.

"The friends should, without too much dwelling on these negative things, be made to understand that some people are spiritually sick and that their disease is, alas, contagious. Some recover from it, as did Mr. … whose heart could not rest till he returned to the fold; others do not. The Master and Bahá’u’lláh have taught us that associating with these souls is not likely to heal them at all, but on the contrary exposes one to grave danger of contagion. The history of the Faith has proved this over and over again. The only way we can prove to such people that they are wrong is to censure their conduct; if we sympathise with them we only fortify their perversity and waywardness."

(From a letter written on behalf of the Guardian to an individual believer, January 23, 1945)

https://bahai.works/Lights_of_Guidance/Believers_Forbidden_to_Associate_with_Covenant-Breakers