What is the ruling on shunning a brother and withholding greetings from him if he is committing adultery and if greeting him leads to his persistence in this act?

Adultery is a heinous abomination and a grave sin. Whoever is afflicted with a relative who commits this abomination should advise him, admonish him, remind him of God and the punishment for disobedience in this world and the hereafter, and direct to him those who will remind him and present to him what will deter him from this act. He should also pray for his guidance. If he does not desist, then boycotting him and refraining from greeting him are permissible, especially if there is hope that this will cure him, or if there is a fear of being influenced by his morals.