“Every believer, even if he is a disobedient sinner [faasiq]– then it is forbidden to boycott him if there is no benefit in that boycotting.
If there is benefit in the boycotting then we do it because at that point the boycotting would be a cure.
But when there is no benefit in it or when it results in an increase in disobedience and insolence–then leaving that which has no benefit is the benefit.”
Fataawaa fil-Aqidah, vol. 2, p. 1098.
(Shaikh Ibn Uthaimeen, may Allaah have mercy on him)