What is the ruling on the evil eye (al-ayn) and envy (al-hasad) in Islam, are they permissible or forbidden, and what is the punishment for the boastful or the one who threatens with it?

You must know the difference between the evil eye (ayn) and envy (hasad). Envy is wishing for a blessing to disappear, while the evil eye originates from the admiration of the beholder (‘ā’in) for something, followed by a malicious soul. Envy is broader than the evil eye; every beholder is envious, but not vice versa. Both are forbidden by Islamic law. Envy is prohibited in the hadith: "Do not envy one another." The evil eye is prohibited due to its causing harm, as the Prophet, peace and blessings be upon him, said: "There should be neither harm nor reciprocation of harm." The beholder who intentionally harms people is sinful. The ruler (walī al-amr) must prevent him from mingling with people and imprison him if necessary. He is also liable for the harm he causes, and it may even lead to retribution (qisās) or blood money (diyah) if he causes death with his evil eye.