Praise be to Allah, and peace and blessings be upon the Messenger of Allah.
Backbiting a non-Muslim is prohibited if he is a dhimmi, or someone who has a covenant or security agreement. As for a non-Muslim who is at war with the Muslims, mentioning him in ways that are permissible concerning him is allowed. It is authentically reported that the Prophet ﷺ instructed Hassan ibn Thabit رضي الله عنه to satirize the polytheists.
It is established in the hadith of the bankrupt person that the Prophet ﷺ said that a person may come on the Day of Judgment with prayer, fasting, and zakat, while having wronged people, insulted them, taken their wealth, and assaulted them. Their rights will then be taken from his good deeds. If his good deeds run out before their rights are fulfilled, some of their sins will be taken and placed upon him, and then he will be thrown into the Fire. This was narrated by Muslim.
This compensation for injustices takes place between the people of Paradise and the people of Hell. Therefore, whoever wrongs another person in this world and does not settle the matter with him may be subject to retribution on the Day of Judgment, whether the wrongdoer is a Muslim or a disbeliever.
However, if the wronged person is a disbeliever, the Muslim will not bear the sin of disbelief or major shirk, because shirk is the greatest of sins, and it is among the matters that invalidate deeds. A Muslim cannot be burdened with another person’s disbelief.
Rather, some of the Muslim’s good deeds may be taken according to the injustice committed, or he may be burdened with some of the sins of the disbeliever relating to other sins and acts of disobedience, according to what is required for the compensation, such as wrongdoing, aggression, and similar offenses. This is because the disbeliever is held accountable for his disbelief as well as for the other sins he committed.
This is indicated by Allah’s statement concerning the people of Hell:
“What has landed you in Saqar? They will say: We were not among those who prayed, nor did we feed the poor, and we used to indulge in vain discourse with those who indulged in it, and we used to deny the Day of Judgment.” [Al-Muddaththir: 42–46]
This indicates that the disbeliever is punished for his disbelief as well as for his other sins.
Therefore: If a Muslim wrongs a disbeliever and does not settle the matter with him, the wronged person may be compensated from the Muslim’s good deeds. If his good deeds are insufficient to compensate for the injustice, some of the wronged person’s sins may be taken and placed upon him. However, the Muslim will not bear the sin of disbelief or major shirk.
The Muslim must therefore beware of wronging people, backbiting them, and violating their rights. He should return people’s rights to them and seek their forgiveness before the Day comes when wealth and status will be of no benefit, and dealings will instead be through good deeds and bad deeds.
And Allah knows best.