Is it permissible to forsake a brother in faith who commits minor innovations (bid'ah saghirah), such asخصص a specific supplication not mentioned in the Sunnah and repeating it, despite the presentation of evidence to him?

Whoever makes a supplication before the takbir for prayer believing it to be a sunnah has innovated (ibtada'a). However, if he does not believe it to be so, he is not judged as an innovator (mubtadi'), and it is not permissible to boycott him. Boycotting an innovator is conditional upon benefit (maslaha); if it is useful and a deterrent, then it is legitimate, otherwise not. Some people may be conciliated, while others are boycotted, depending on the benefit.