Is it permissible for a Muslim – in the absence of a Muslim ruler – to forbid evil with his hand, based on the action of the Prophet, peace and blessings be upon him, when he removed a gold ring from a man's hand?

Enjoining good and forbidding evil is one of the rituals of religion. It is a collective obligation (fard kifayah), and at times it becomes an individual obligation (fard ‘ayn) depending on one's capacity. A Muslim must enjoin and forbid according to their ability: with their hand, and if they cannot, then with their tongue, and if they cannot, then with their heart, and this is the weakest of faith. The order of these levels is fixed and cannot be reversed. Changing evil does not depend on the presence of a ruler. The Prophet, peace and blessings be upon him, changed evil with his hand because he was the supreme ruler, and this is one of his unique characteristics, so changing evil was an individual obligation upon him that could not be relinquished.