Is backbiting a non-believer, such as describing him as ill-mannered, considered prohibited backbiting that necessitates repentance, and is it the same as backbiting a Muslim?

Backbiting is forbidden, whether it is against a Muslim or a disbeliever, if the latter is a Dhimmi. However, it is permissible concerning a belligerent disbeliever, provided that only the truth is spoken. Some scholars have permitted backbiting a disbeliever, such as Ibn al-Mundhir and al-Bukhari. The phrase "ill-mannered" constitutes backbiting unless it refers to someone who has wronged you through their bad manners. Backbiting is a major sin when it concerns a Muslim, and less severe when it concerns a disbeliever, and some scholars have permitted it in the latter case. The prohibition of backbiting is established by the Qur’an, Sunnah (definition), and scholarly consensus. It is defined as mentioning your brother with something he dislikes. Scholars have differed on whether it is a major or minor sin, but it is better to abandon backbiting and occupy oneself with what is beneficial.