Is shunning a friend who caused harm and "slander" for a year, while refusing to renew the friendship out of fear of their past behavior recurring, considered the kind of shunning that prevents good deeds from being accepted, and does it entail sin?

We advise you to seek refuge (with Allah), maintain your remembrances (dhikr), and ask Allah for well-being. There is no objection to keeping your distance from this man if you do not feel secure from him reverting to his old habits. However, you must cease shunning him by greeting him with "peace" (salam), based on the Prophet's (peace and blessings be upon him) saying: "It is not lawful for a Muslim to shun his brother for more than three nights, with each turning away from the other when they meet. The better of the two is he who initiates the greeting of peace." We also advise you to accept his apology if you observe his sincerity, as forgiveness is a characteristic of the noble. Allah the Almighty said: "and those who restrain anger and pardon people—and Allah loves the doers of good." There is no objection to asking him to apologize in front of your friends and to retract his slanderous statements.