What is the ruling on responding to abusive language, insults, and mockery of religion on social media?

It is permissible for the one who has been insulted to retaliate against the insulter in kind, based on the Almighty’s saying: "So whoever has assaulted you, then assault him in like manner as he assaulted you." Excluded from this is anything that is inherently forbidden, such as declaring someone an unbeliever (takfir) or lying. Forgiveness is better.

As for the one who mocks religion, he should not be retaliated against in kind, because that may lead to insulting religion itself or increase his mockery. The best approach is to advise him and clarify the truth to him, or to refer his matter to the judiciary if possible, while refuting the specious arguments and fabrications he raises.