How can one abandon someone whose negative influence on religion is feared?

The fundamental principle is the prohibition of shunning a Muslim for more than three nights, except for a legitimate Shar'i reason, based on the Prophet's (peace be upon him) saying: "It is not lawful for a Muslim to shun his brother for more than three nights. They meet, and this one turns away, and that one turns away. The best of them is the one who initiates the greeting." However, scholars are of the opinion that there is no harm in shunning someone whose company is harmful, and from whom one fears harm to their religion. Indeed, keeping a distance from such a person is better than associating with them. This is what is called "beautiful shunning" (al-hajr al-jameel), which is limited to ceasing association without adding harshness or harm, and upon this, the scholars have reached a consensus.