What does islam says about cursing each other?

there is hadith about this which says ( The Messenger of Allah (PBUH) said, “Reviling a Muslim is Fusuq (disobedience of Allah) and killing him is (tantamount to) disbelief.’’ [Al-Bukhari and Muslim].

وعن ابن مسعود رضي الله عنه قال: قال رسول الله:

متفق عليه

This hadith is an explanation and follow up of the previous hadith of the three signs of a hypocrite; specifically the clause “and when he quarrels, he abuses.”

Definitions of terms:

In the hadith, the Prophet (salallahu ‘alayhe wasallam) uses the word “سب”, which means cursing and cussing (reviling).

Ibn Taymiya’s definition of سب: “Words to belittle or degrade a person and (even if one doesn’t say it directly) it is understood that one’s trying to degrade regardless of language or culture.”

Definition of فسوق: “Fusuq” literally means someone going astray or deviating from the right path. It is like taking the central part of a fruit out, so that it cannot grow properly anymore.

The Islamic definition is as follows: “Fusuq”: a name given to someone who persistently commits a major sin and doesn’t repent.

So from this hadith, it is apparent one who curses a Muslim is a fasiq (فاسق).

2. General lessons from the hadith:

This hadith teaches many things:

It describes how respectful and honorable a Muslim is.

It tells us Fusuq is less than kufr. The Prophet (salallahu ‘alayhe wassallam) separated the two (reviling a Muslim and killing) and gave each a different name.

This hadith is an answer to khawarij (خوارج) sect, which believed that if a person commits a major sin he becomes a kaafir. On the other hand, a fasiq (one who commits a major sin) is still a Muslim, and does not take him out of the fold of Islam.

3. Killing a Muslim is an aspect of Kufr.

3. Other verses and hadith that relate to this matter:

The Prophet (sal allahu alayhe wasalam) said: ليس المسلم بالطعان ولا باللعان ولا بفاحش ولا بذئ

“The Muslim is not an accuser, curser, curser with evil tongue (big curser), or minor curser”

The Prophet also said, “Whoever curses a Muslim is like killed him. Whoever accuses another Muslim, then it is also like killing him.”

This hadith proves how grave of a sin it is for one to accuse or curse his fellow Muslim brother. For one who does this, receives the same punishment of one who actually kills another Muslim.

Surat al-Hujurat: 11 ((الحجرات يَا أَيُّهَا الَّذِينَ آمَنُوا لَا يَسْخَرْ قَومٌ مِّن قَوْمٍ عَسَى أَن يَكُونُوا خَيْرًا مِّنْهُمْ وَلَا نِسَاء مِّن نِّسَاء عَسَى أَن يَكُنَّ خَيْرًا مِّنْهُنَّ وَلَا تَلْمِزُوا أَنفُسَكُمْ وَلَا تَنَابَزُوا بِالْأَلْقَابِ بِئْسَ الاِسْمُ الْفُسُوقُ بَعْدَ الْإِيمَانِ وَمَن لَّمْ يَتُبْ فَأُوْلَئِكَ هُمُ الظَّالِمُونَ

(Talks about nicknames, and gesturing) O ye who believe! let not some men among you laugh at others: it may be that the (latter) are better than the (former): Nor let some women laugh at others: it may be that the (latter) are better than the (former): nor defame nor be sarcastic to each other nor call each other by (offensive) nicknames: Ill-seeming is a name connoting wickedness (to be used of one) after he has believed: And those who do not desist are (Indeed) doing wrong. (49:11)