Is it permissible to curse Satan, and is it permissible to insult and slander as a joke?

We have not been commanded to curse Satan, nor have we been forbidden from it. It is a foregone and established matter, as Allah Almighty says: "And indeed, upon you is the curse until the Day of Recompense," and His saying: "Allah has cursed him."

Engaging in cursing him is not beneficial; rather, it may increase his arrogance, as in the Hadith of the Prophet, peace and blessings be upon him: "Do not say 'May Satan be disgraced,' for he magnifies himself until he becomes like a house and says: 'I overpowered him by my strength.' But say: 'In the Name of Allah,' for he shrinks until he becomes like a fly."

Therefore, Allah Almighty commanded seeking refuge from him, as it is the only way to get rid of his cunning and whispers. Allah Almighty says: "And if an evil suggestion comes to you from Satan, then seek refuge in Allah. Indeed, He is the All-Hearing, the All-Knowing."

As for insults and slander, they are forbidden, whether serious or in jest, and they are not befitting of a believer; for the Prophet, peace and blessings be upon him, said: "The believer is not one who slanders, or curses, or is obscene, or vulgar." A Muslim must keep his tongue pure from every evil word and adhere to beneficial speech, for everything he says is recorded and he will be held accountable for it.

As for slander, whoever slanders a chaste man or woman and does not bring four witnesses, the prescribed punishment must be applied to him, for Allah Almighty says: "Indeed, those who accuse chaste women, unaware [of the evil], believing – are cursed in this world and the Hereafter; and for them is a great punishment," and His saying: "And those who accuse chaste women and then do not produce four witnesses - lash them with eighty lashes and never accept from them testimony, and those are the defiantly disobedient."

Therefore, one must control their words before they are uttered, lest they become a cause for misery in this world and the Hereafter.