Is the questioner sinful for shunning an old friend who used to abandon prayer, then grew more averse to religion, to the point of mocking God's rituals, knowing that the friend thinks the shunning is due to a worldly dispute, while the questioner fears the warning mentioned in the Hadith: "The gates of Paradise are opened on Monday and Thursday, and forgiveness is granted to every servant who does not associate anything with Allah, except for a man who has a dispute with his brother. It is said: 'Wait for these two until they reconcile'"?

If your companionship with him is based on the hope of his reform, coupled with continuous advice, then there is no harm. He erred in his ill-conjecture, and verification was incumbent upon him. A person in this state does not deserve your companionship, and it was your duty to advise him when he mocked religious matters, for the Messenger of Allah, peace and blessings be upon him, said: "Whoever among you sees an evil, let him change it with his hand; if he cannot, then with his tongue; if he cannot, then with his heart — and that is the weakest of faith." Boycotting him is permissible and may sometimes be obligatory, and one should consider the Islamic benefit in doing so.